Why does my Samsung Galaxy S3 with 4.3 run so slow? I live in South Africa and we recently received the 4.3 update for the Galaxy S3. When I  perform general functions on the phone (open apps, browse web, run multiple apps), everything goes very slow. As an example, if I push the home button, the apps on my home screen are gone and then return again after a while.

Why would this update do this to my phone? How can I increase the performance of my device which now runs on 4.3?
This is because of the update not being done on a clean install. Also Samsung phones have TouchWiz overlay on android which is a bit heavy.

To make your phone fast do a full factory reset after taking a full data backup so that you can restore everything! Doing this would clean up any mess left behind by the update process.
Always try and do a clean install for a major update.