Hi and welcome
I guess by now you have either stopped or not stopped the update! Hopefully not.
An update, depending upon what it is, overwrites the system files that are needed for your phone to work. Stopping it (by turning off, removing battery etc) is quite likely to leave you with a phone that does not work any more. A system update completed without interruption should not affect any of your data, pics, files etc.
I guess this is to late for you (either way) but may inform someone else
Roger