How to change the battery of my sentry saf...

see
http://www.sentrysafe.com/pdfs/OwnersManuals/172967.pdf

You must replace the batteries located in under the keypad.

Use a large paperclip to unlock the cover. Push the paperclip into the small hole while at the same time, sliding the battery cover to the right. Gently remove the battery housing and replace batteries. You will have to reset your password again, but can find the directions to do so by going to the Sentry site: http://www.sentrysafe.com/pdfs/OwnersManuals/172967.pdf,