I bought a second hand 5C. How do I unlock it?

Define "unlock".

If it's carrier locked, only the carrier it is locked to can authorize unlocking it.

If you've encountered Activation Lock, the owner of the account used to lock it will have to remove the lock. There is no way to bypass activation lock.

If you mean a carrier lock, ask the carrier.

If you mean the activation lock, you’ll need to contact the person who set it; send them this link.

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