First, check that your machine is suitable for Snow Leopard. It needs to be Intel core 2 duo based.
Minimum specs for Snow Leopard. Mac OS X v10.6 Snow Leopard -Read the Technical Specifications
To buy the DVD, if you are from the USA go to
In Europe or otherwise substitute your national code in place of /us above.
Note. In the UK … the last known price was £14.
Before you start upgrading, back up your files.
Once you have upgraded to Snow Leopard you will need to apply the Combo updater. Mac OS X 10.6.8 Update Combo v1.1 and follow with a software update to pick up any later updates.