I had this issue when I was trying to install apk on emulator and I was always getting error messages that I need to uninstall the old version of my app’s apk.
I solved it like this:
1. File -> Settings -> Build, Execution, Deployment.
2. Instant Run -> disable “Enable Instant Run to hot swap code/resource changes on deploy”.
3. Apply -> OK
After that you can clean the project (Build -> Clean project) and re-enable instant run to get the instant run working again.
EDIT (Android Studio 3.0)
Disable Instant Run (Android Document)
To disable Instant Run:
- Open the Settings or Preferences dialog. (For Mac, Android Studio -> Preferences)
- Navigate to Build, Execution, Deployment > Instant Run.
- Uncheck the box next to Enable Instant Run.