What Should I Charge Someone For Updating Their Website?

This is a subjective matter. It depends on what the company/person can afford, how much you need to get the job done, and how much other, similar services charge.

Check the area consulting services. Find out how much they'd charge, then under cut that by 15 - 20%. This ensures that a better deal won't be found and that you don't have to be held to their standards.

If I already have the tools necessary to complete a job, I'll normally charge $50 - $60 / hour. That lets me make approx 90K/yr and still pay my taxes.