My OS is still 10.6.8 because I just got my logic board replaced by another one, cause mine had a problem and the computer didn't work for 4 years.

I just got it back and from what I can see I should be able to install High Sierra or another OS but it says it doesn't has anything to update and through app store High Sierra asks 10.8 or recent to be able to be installed.

How can I upgrade my mac out of 10.6.8?