No easy way.
If you have no backup of your previous system and data, you basically have to erase your Mac's internal hard drive and install OS X Snow Leopard from scratch as a clean install and run all software updates as well as reinstall all of your applications and any updates.
You will now need some way of backing up all of your important data. Backup data to CD/DVD, large capacity USB flash drive OR an external hard drive.
If you have/had an external hard drive with a complete, copy (cloned ) backup of your previous system, then the doing is/was a lot quicker and simpler.