If your Wells Fargo credit card expired, you should have already received a new one in the mail a few weeks before the expiration date listed on the card. If you didn't receive a new card in the mail and your Wells Fargo credit card expired, you should contact customer service as soon as possible. They'll be able to tell you whether your new card was sent out, and send you a new one if it got lost in the mail. The number for customer service is 1-800-642-4720.
Once you have received your new Wells Fargo credit card, you'll need to activate it by calling the number on the sticker attached to the front of the card. After that, the new card, which will have the same account number but a new expiration date and security code, will be ready to use. Make sure to dispose of the old card by cutting it up for security.