Q: upgrading from 10.5.8 to 10.7

To see if your Mac is supported, check your MacBook model > http://support.apple.com/kb/HT4132?viewlocale=en_US&locale=en_US

If you have a Mid 2007 or newer MacBook Pro, you can run OS X Lion and Mountain Lion. If you have an older Mac with an Intel Core 2 Duo processor, you can use OS X Lion with the MacBook

Lion requires at least 2 GB ram, and an Intel Core 2 Duo, i3, i5, i7 or Xeon preocessor.  If you qualify, you need to first buy Snow Leopard, available from the Apple on-line store, for $20, install and update to 10.6.8.  Then you can go to the Apple phone store, 1-800-MY-APPLE and purchase a download code ($20) to use with the App Store to donwload 10.7.5.