You have posted in Using the Community which is for questions about using these forums. Which Adobe app or service is this question related to please?
Your computer's File Manager is used to rename files. Use either Win File Explorer or Mac Finder.
As a rule of thumb, file names should be ≤ 128 characters in length including 3 character file extension. However on older FAT storage systems there is a total character limit of 11 including extension -- xxxxxxxx.ext
Hope that helps.
Nancy O'Shea, Adobe Product User & Community Professional Alt-Web Design & Publishing ~ Web : Print : Graphics : Media