How I can find out what the latest version of OS X is available for me?

Hello, I would like to update my OS, ideally to at least 10.7. When I try to download Yosemite I am told it 'Cannot be installed on this computer'. I would like to find out what the latest version is that I can install. Can anyone tell me, or tell me how I can find out? Thanks, D

I am currently running 10.6.8.

Here is my spec:

Model Name: MacBook

Model Identifier: MacBook2,1

Processor Name: Intel Core 2 Duo

Processor Speed: 2 GHz

Number Of Processors: 1

Total Number Of Cores: 2

L2 Cache: 4 MB

Memory: 2 GB