I have version 126.96.36.199 and I wanted to upgrade to the newest version. However, I am afraid it will break my theme for my store. Is there somewhere where I can see the changes applied? Thanks
It will break your 1.7 theme. There are some changes like the addition of the formkey in a lot of template files.
I just found this which should help you out:
Create a development server, move your site over, upgrade your theme as above, then do a test upgrade and see how things go.