Scared to Upgrade from 3.4.2 to 3.5.1

Im scared to update from wordpress 3.4.2 if i do this update will it change how my site looks i believed i try’d this and it messed up the look of the whole site and i had to quickly find a way to down grade back to the old version. If you have any clue if this will happen and how to update and not change the look of my site please let me know. All help is appreciated.

The blog I need help with is lacrosse-lounge.com.