10.7.x has not been available for years, many generations of OS X and now Mac OS have been released since 10.6.8. When new versions are released Apple normally does not make previous versions available.
If your computer has the ability to be upgraded beyond 10.6.8 please provide more information. What we need to know is the year and amount of RAM installed. You can find this information out by clicking the Apple symbol in the upper left corner of the display and then select About this Mac.
We can provide you some guidance however without basic information it's difficult for us to do so.