You will be redirected to a page showing all the collections you have created. Select the collection that the NFT you'd like to update belongs to. You then need to select the tab named Smart contract.
This will open up a new page with different smart contract functions. Select Advanced functions.
A menu will open up. Select set-token-uri in the list of smart contract advanced functions. You are then required to input the token ID of the NFT you would like to alter, as well as the name of the NFT, the asset, the attributes and the description if required. Please always double check you have selected the correct collection, and entered the correct token ID. If you're unsure of the token ID, it can be found in the URL of the given NFT page.
Once you’ve clicked publish, the wallet transaction will pop up. Confirm/sign the wallet transaction, and when this transaction is confirmed on the blockchain, your NFT’s metadata will be changed.