Yes you can. If the auction has not yet started you can find all your max-bids in your My Pickles account (click on My Bids and navigate to the My Bids for PicklesLIVE page). Here you can modify & even remove your max-bids.
If the auction has started, you will need to login to PicklesLIVE and modify the max-bid on the asset directly. If you reduce your max-bid while being the highest bidder, the change won’t affect your current bid but it will apply if another bidder places a higher bid. If you increase your max-bid, the change will take effect unless the lot has already been sold. Note that if you're the highest bidder, removing the max-bid won't reduce your current bid but no further bids will be placed on your behalf if another bidder participates.