You can't upgrade to the most current version, as the most current version is Mountain Lion. It requires a MacBook 2008. Other models only require 2007 release, but not MacBook. Upgrading to Lion is a possibility, but you need to be aware of these pitfalls:
And unless you are lucky enough to find someone with the 10.7 USB Flash drive, you'll need to purchase 10.6 first from the Apple Store on DVD before upgrading to 10.6.6, and then 10.7 via App Store download.
As for performance, if there is a problem, now, it will remain or get worse when upgrading to 10.7. First thing to do is make sure your system is healthy and functional now before updating, and before that even is backing up your data at least twice.