What's the best procedure for installing Lollipop 5.0.2?

[AC Question]

My phone is a Samsung Galaxy Alpha and the update is already downloaded.

 

[Rukbat]

Then it should install. (If you downloaded it from some site, make sure you checked the MD5 of the file with the one listed on the site. Then the best way to install it is to follow the instructions on the site. It could be a tar or tar.md5 file, it could be a zip file - we don't know, and what you do depends on that.)