To update the price of a listing, navigate to your profile by clicking the drop-down next to your wallet address in the top-right of the page and then click "View Profile"
From there, click into the tab that says "Listed items".
The default view will be folder view, which will group your NFTs based on collection. If you wish to update multiple NFTs from different collections you can do so by first toggling into the "list view" on the right-hand side of the page. This will display all your NFTs individually.
Click on the NFTs that you wish to update and watch them populate in a widget to the right of the screen. You can adjust the prices individually or set a global price if you wish to update them to all be the same price. Click "Update Listing now" when you are ready.
In order to cancel listings you will need to click on "Details" to get to the NFTs item details page.
From there you can click "Cancel listing" and that should cancel the listing for you. Note you can also change the price from this page if you wish to do so.