Android Studio: Installation failed since APK was not signed

Question

I am attempting to run my app in an emulator and have been receiving the following error:

Installation failed since the APK was either not signed, or

Answer 1

I solved it more or less following the answer of Alex K above, but did not know where to look for 'settings' (total beginner!).

So go to the AVD manager (icon of mobile in toolbar) and click on the arrow on the far right, a small menu appears and here you select 'Wipe Data'.

You do need to first close the emulator.