Phone keeps turning off

My phone keeps turning itself off. Its been maybe 5 days and sometimes it will go 4 hours without doing it, and today I cant even get it to the main page before it shuts down again. I dont have to remove the battery to get it to turn back on, it will turn on if I press the button but eventually turns off again. Ive tried taking the battery out.

I need to update my phone but I cant get it to stay on long enough to do it. I went to my local sprint store and they are no help what so ever. They just told me to figure out a way to update it :/ Jee thanks..... They were so unprofessional and rude and could not help. There is a store about an hour and a half away that I go to that usually is helpful but I want to avoid it if I can.

Do you think it is shutting of because of the update thats needed?
Any suggestions?
Ive searched around but cant find any situations that are exact to mine

Thanks!