Note: The ENS App and ENS Explorer are both currently on Sepolia testnet. Behaviour and available features may change before mainnet.
Changing a resolver swaps out the contract that answers questions about your name. Registering a name sets a resolver on it already, so most people never need to change one. You'd do it to move to a custom resolver, or to replace one that isn't working.
Steps
Note: onchain changes cost gas — the network fee Ethereum charges to process a transaction. It is paid in ETH from your connected wallet and goes to the network, not to ENS. Your wallet shows the exact fee before you approve.
Connect the wallet that owns the name. You'll need a little ETH for gas.
Open the name in ENS Explorer and go to the Resolver tab.
Click Change resolver. If you can't see it, you're either not connected as the owner, or the name has no resolver yet. Go straight to the Change resolver page for the name.
Choose how to set the resolver. Three options, below. If you're unsure, deploy a new permissioned resolver.
Click Save Changes and approve in your wallet. Deploying a new resolver takes two transactions, so you sign twice: once to deploy it, once to point your name at it.
Check the Resolver tab. Once both confirm, it fills in with the resolver's details. You can now edit records on the Records tab.
The three options
Deploy new permissioned resolver: the safe default. Turn Use custom resolver off. Explorer deploys a fresh audited resolver and points your name at it. You don't have to find or paste an address.
Use custom resolver. Paste any contract address. Use this only when you know the address of a resolver you trust.
Existing permissioned resolver. Pick from resolvers you've already deployed. If the list won't load, deploy a new one instead. See What do I do when a transaction goes wrong in ENS Explorer?
Important: Explorer does not check that a custom address is a real resolver. Paste the wrong thing and your name stops resolving, with no error to warn you. Double-check the address before you save.
Check the interfaces before you switch
A custom resolver can be a real, working contract and still not handle every kind of record. That failure is quieter than the one above: most of your records keep working, and only the unsupported ones go dark.
Open that resolver's own page in ENS Explorer (its contract address links straight there) and read the Interfaces list. If the record type you need isn't on it, that record stops resolving the moment you switch, and nothing tells you.
Common questions
How long does it take?
Each transaction confirms in a block or two on a quiet network. Busy networks take longer. The Transaction Manager shows progress. See How does the Transaction Manager work in ENS Explorer?
Can I undo a resolver change?
Yes. Open Change resolver again and set it back. Records on the previous resolver are still stored there (they just weren't being read while another resolver was active), so switching back restores them, as long as nothing else has touched them. Check your records after any change.