If you're experiencing problems, back up as much data as you can (especially important stuff, photos, documents, etc) to your computer. Once you've done that do a factory reset (which will wipe everything including apps and data). Once the phone boots back up it will be running Lollipop as it is now but it will have done a clean install - which from my experience on Android and Windows machines is ALWAYS the best way to do an update if possible.
Whenever I can I always do major updates on a clean install. I seem to have fewer problems and conflicts in the long term this way. (Or maybe it doesn't really make that much of a difference but either way I have peace of mind of starting fresh!)