Develop Reference

Is it possible to build a free version and paid version of your app and have the paid app replace the free one on the user's device?

I've already made two different Android projects and they have different package names. They're identical except in the Main Activity where the free version expires after 7 days whereas the paid version checks for a purchase license.
What I want is that when a user installs the paid version then the free version on their device (if it exists) gets replaced by the paid version and also all the user's saved SharedPreferences from the free version move over to the paid version. Is this possible? Or will the user have to uninstall the free version as well as lose all their saved settings?
I read questions related to this and they all talk about using ProductFlavors to create different build variants, but I'm not sure if the purpose of this is just to make the work easier for devs or if it helps in what I'm trying to do.

Yes, if make it like update, replacing old app with new one.

Linking between paid and free app in the Play Store

In Android Studio I have two "flavors" of the same app, one is the free version with some functionality removed, the other is the full version with some extra bells and whistles thrown in.
When I am in the Google Play console, do I have to maintain two separate projects but just use the free-release apk for the free project, and the full-release apk for the paid version?
If so, how do I know ahead of time how to give a link from the free version to the paid version if I don't yet have any sort of URL or method for going there?

If you are referring to knowing before which URL should you add to your free app to redirect users to your paid app, then you can use the general convention that the Google Play employs
https://play.google.com/store/apps/details?id="packagename"
So you can give your packagename of your full app

Changing from a free to a paid app

I developed an Android app and added it as a beta app to the play store. Then I discovered that my beta testers would have to buy the app, so I changed it to free (oops). I now understand that I can't change a free app to a paid app and that I need to add a new app to the developer console.
However, when I try to add a new app, the Google Developer Console reports that the title has already been used (obviously). But that's the name I need (i.e., I have the same-named app available on other platforms). What should I do? If I delete the existing (beta) app will it let me reuse the name? I don't want to try doing this without knowing, because I suspect I'll break the versions that are being used by my beta testers.
Thanks!

Make sure to use a different package name for your paid version. Rename the free beta version and then use the intended name for the paid one.

changing app from free to paid in android, how does this affect previous downloaders?

So Ive decided to turn my free app into a paid app, the question I have is how does this affect people who previously downloaded my app, for example If I release an update in the future will the people who already dowloaded the app when it was free have to pay to download the update? this I would like to avoid as I dont want bad ratings in android market, thanks in advance!

Once an app is free on the Android Market it cannot be made a paid app. You can unpublish it, and you can publish the app under a new package name for a fee, but your existing users will not auto-update to it.

#mah is right, though there is a way around that limitation - instead of replacing your free version with a paid version, you could implement in-app purchasing to license the additional functionality. Now, you can have the free, limited version and it is simple for the user to upgrade within the app to the full, paid version.

Upgrading free to paid Android apps without leaving two icons

I have an Android app with free and paid versions, where the free version has a time limit, after which it redirects users to the Market to buy the paid version. The two versions have different package names and are submitted to the Market as separate applications.
However, when users buy the paid version, this doesn't replace the free version - they're left with both versions installed at once. I'd like it to install over the free version. Ideally it would also replace any existing shortcuts on the home screen with shortcuts to the new version, but that's less important.
Is there an elegant way to handle this?

You can't have the free version automatically deleted when a user buys the paid one. Only the user of the device can uninstall applications from the phone, and he must do so manually.
If the two icons thing really bothers you, you could always switch to a free version model only, using in-app billing to unlock features or contents in your app.

A popular way to handle this situation is to only release one fully-functional package.
Put all of the functionality into the "free" version, and then release a "Pro Key" which is just an empty package. Then you can add a function to the free version which checks whether the Pro Key is installed. You can then use this function to selectively unlock certain features of the application.
See How can I use the paid version of my app as a "key" to the free version? and Detect if app was downloaded from Android Market for more info about this process.