UPDATE
In Android Studio Version 3.5 and Above
Now Instant Run is removed, It has "Apply Changes". See official blog for more about the change.
we removed Instant Run and re-architectured and implemented from the ground-up a more practical approach in Android Studio 3.5 called Apply Changes.Apply Changes uses platform-specific APIs from Android Oreo and higher to ensure reliable and consistent behavior; unlike Instant Run, Apply Changes does not modify your APK. To support the changes, we re-architected the entire deployment pipeline to improve deployment speed, and also tweaked the run and deployment toolbar buttons for a more streamlined experience.
Now, As per stable available version 3.0 of Android studio,
If you need to turn off Instant Run, go to
File ? Settings ? Build, Execution, Deployment ? Instant Run and uncheck Enable Instant Run.