As for the question...
It's not so easy. Android is not like Windows where you have a list of installed updates that you can remove. Once an Android system update is installed it's done. Even if you factory reset the phone, it only wipes the user data and reverts to "factory" settings for the NEW version that's installed.
Depending on your phone, you MAY be able to revert to a previous version if the manufacturer has made the images and tools available. This WILL result in a wipe of the device. However, you will get prompted for the update again.
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