You can not upgrade to a Photoshop Version lower than CS3.
Adobe stops selling them and stops the upgrade process.
And from 3.0 you can only upgrade to 7.0 and need to upgrade another time to 8.0
But as both can not be bought anymore, you can not upgrade anymore most likely.
Adobe stops selling them and stops the upgrade process.
And from 3.0 you can only upgrade to 7.0 and need to upgrade another time to 8.0
But as both can not be bought anymore, you can not upgrade anymore most likely.