Scared to upgrade

Hi guys

i want to upgrade but im scared to do so. I have some custom made areas, and i have a language over ride file also.

The override file some how doesnt cover all fields, i noticed in the override file i have for example 10 copies of one word occurring, while in the language file theres 14.

This causes me to need to change the override file, test everything, and than also change the original language file.

Is there a way to do updates thats more fail proof? Im scared i will end up reprogramming everything for 3 days after the upgrade and i really dont have time for that.

So .. upgrade but not loose language file, and not loose customisations.

Thanks