When you perform an update on the Play Store, you must upload a new one
.apk. This new file can be what you want, even a completely different game, so if you know how to make two versions of the game, one with unlocked levels and one with blocked, this should not be a problem.
The player who has reached the 8th level must play from level 1 after the
If "unblocking" means that you want to delete the saved file from the player, to start over again, this could be complicated. I do not know any way to delete the files saved in the update, but when saving data you can add a version prefix to the key, something like "v1.0-level", so when you update, the application will look for "v1.5- level "and fails, forcing the player to start over.