How to safely upgrade iMac9,1 to Mavericks

I have an iMac 9,1 (now using OS X 10.6.8; 2.66Ghz Intel Core Duo; 2GB 1067 MHz DDR3).

Would like to upgrade to newest OS (Mavericks) but do I have to upgrade to the previous version first?

I need some software that requires OS X 10.7 but am am hesitant because this machine is "old" and I don't want to lose too much. What kinds of software will be incompatible if I upgrade?

Present software includes quite a few titles that did not come from Apple Store.

Any guideance would be appreciated!

Thanks