If the update is laggy, the best way to fix this is to backup the device and do a factory reset. This will take care of any lag or issues the phone had.
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As per your priorities, get rid of unwanted applications and also make sure that your internal storage is not fully filled. Restart your Galaxy device, once in a while. Install and use lite version apps. Most likely, if you follow the tips & tricks mentioned above, it will definitely resolve the lagging issue.
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