If you donated more than $1 USD before the price change, then in your "my collections" page, at the top there is an area showing games that you own. There is a download link there.
If you did not donate at least $1 USD before the price change, then you sadly don't "own" the game because you didn't pay for it, and will need to pay the $8.99 price to gain access to the new updates.
Hopefully this clears things up for you.
Edit: fixed some wording issues for clarity.