Default upgrading twrp evo 4g lte

can someone explain how to upgrade from twrp 2.1.8 to 2.2.1? is it necessary? i see where some new roms call for being on 2.2.1 as a preference. and if someone can explain, how do i keep my nandroid backups? i have searched i just havent found a clear cut answer. and im very worried about losing my original backup. i am s-on rooted and did take the ota. ive been using meanrom v2.0. i was thinking bout trying viper 4g and it states in the installation instructions twrp 2.2.1 would be best. i would like t be on the latest recovery regardless. thanks to those who may help.