Its possible to change your NFTs metadata after its minted, but the process is complicated: you´ll need a deep understanding of NFTs and Blockckchain tech to do it.
The need to change the NFT metadata can be triggered by many factors: errors, change of specs etc. but in general the process is as follows:
– Go to Etherscan.io and locate the transaction of your NFT.
– Click the contract tab
– Click Read Contract
– Find the token URI and enter your NFTs token ID in the provided box.
– This will display the properties of the NFT as a string of letters and numbers: copy it.
– This will take you to the page where you edit the metadata of the NFT.

In here you´ll need coding knowledge to make changes to the metadata. Notice you will need a few more steps if the NFT is a video, gif or other moving image.

NFTs metadata is not advisable to be changed for art NFTs, but for other types such as functional of gaming NFTs you may need it. Just make sure you understand the implications of it.

The fact that the NFT may have been sold does not change all this NFTs while technically stored in user´s wallets are always connected back to the corresponding blockchain. This means that changes to the metdata of the blockchain will automatically update the NFTs in user´s wallets.

Things that can´t be changed in an NFT
The token ID and the contract address, as these are the coordinates in the blockchain of the NFT. If you really need to change those its way better to destroy the NFT and mint a new one. Minting can be expensive: you need to keep in mind always optimization and minimizing mistakes.