Creators are able to update the reserve price of their NFT up until the point of the reserve price being met.
If your reserve price has been met you will not be able to change the price.
How to update your reserve price:
Click onto the NFTs page and there is a drop down menu next to the "Add Price" button
Click "Update Reserve Price"
Enter the updated reserve price
Finalize your price by clicking "Update Price"
When clicking "Update Price", your connected wallet will prompt you to confirm the transaction by paying the gas fee required to complete the process.