Upgrading from 10.5.8 to Snow Leopard 10.6.3 - I've backed up my mac with timemachine / external hard drive. Am I all set to go? Bit nervous!

Hello kind support people - I'm not hugely technical so would appreciate any advice, I'm very worried about my i-photos and loosing them. All my important documents are already on google drive so that's ok if anything has gone wrong. Does all the information stay on my mac (such as photos and mail etc) when I upgrade? Am I likely to experience any difficulties or should I be doing anything else? Yesterday I used time machine for the first time, I have an external hard drive with back-ups taking place all the time (completed yesterday over a couple of hours). Can I just eject the hardrive now and put my upgrade disc in?

Thanks in advance 🙂