I need help in updating my Powerbook G4 15"

I'm not all too savvy with computers...

I am a graphic designer and have a 15" Powerbook G4. It's about 7-8 years old and still running well. Before I used to run games on it, but cleaned it out and only use it for design purposes.

The only problem I have is that the operating system (10.5.8) is too old that I cannot update browsers and use it effectively and efficiently like my desktop PC. Is it possible to update/upgrade my operating system for this notebook? And if it is possible and I decide to upgrade my system, will I lose my Adobe CS4 in the process? I unfortunately lost the program CDs when I moved across the country and have been treating my laptop as if it were gold. I cannot lose my programs since it's all I have and what I use to make a living.

Thanks!!