Backwards compatibility

Backwards compatibility

Hi
I just started working with jQuery at the company I work for. I turns out out software is using version 1.6.3. which is 4-5 years old...
I'm looking in to how problematic it would be to upgrade to a newer version.
Are there any documentation on backwards compatibility or upgrade guidelines?

Do you have any idea to what version it would be somewhat easy to upgrade to?

Thanks a bunch 
Anders