How can I downgrade from Mountain Lion to Lion? Possible Duplicate:
  How to revert to Lion from Mountain Lion?  




How can I downgrade from Mountain Lion to Lion ? I need to download Lion again... thanks
I suggest you to do a complete backup with time machine, then formatting, install lion and restore all the data (including application and preferences) from time machine backup.

If you cannot download lion from app store, you have to search it on the web....