how to update from 10.5.8 to Mountain lion

In the recent past it has been possible to buy Snow leopard from the Apple store but there seems some doubt of late. You may have to buy from eBay.

What is fact is that you need to go from where you are to Snow leopard before you go further ... and then it depends on the machine you have. Minimum specs for Snow Leopard.

http://support.apple.com/kb/SP575

Apple said that customers can still purchase a copy of Snow Leopard or Lion from its online store's telesales agents: 1-800-MY-APPLE (1-800-692-7753) or Customer Service and Sales Support at 1-800-676-2775.]. For Lion you'll get a redemptions code and need to DL from the Mac Apple Store (requires SL 10.6.6+.

thank you