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.