Q: how do I update to the latest OS from 10.5.8

First step is to call Apple at 1-800-MY-APPLE and order a copy of Snow Leopard, 10.6 for $20, install and then on-line software update to 10.6.8.  You can then go to either Lion, 10.7 by purchasing a code to download that from the same phone number for $20, or if your computer is in the compatible list at http://www.apple.com/osx/specs you can just go to the Mac App Store and download Mountain Lion, 10.8.2 for $20.

Your Mac OS X version is 10.5, Leopard. First, install RAM to your computer > http://support.apple.com/kb/HT1423

http://support.apple.com/kb/sp575 If your Mac is compatible, call Apple to buy Snow Leopard. Make a backup, insert the DVD and upgrade. Finally, go to  > Software Update and update to the latest version.

http://www.apple.com/osx/specs If your Mac is compatible, open App Store and purchase Mountain Lion. See if your programs are compatible > http://www.roaringapps.com