If coming from ANY TW lollipop, full wipe is highly recommended
Full wipe means: Wipe cash, Wipe davlik cash, Format data, Format System
Make sure MD5 is matched
Flash the ROM zip
Then Flash OTA Update
If coming from Kit Kat or any non-TW ROM, flash stock Lollipop from here
Root it with CF auto root or flashing any Custom recovery using PC Odin (Philz/TWRP)
Make a full wipe in recovery
Full wipe means: Wipe cash, Wipe davlik cash, Format data, Format System
Make sure MD5 is matched
Flash the ROM zip
Follow in Aroma choose whatever you want and wait until installation is done
Then Flash OTA Update