It depends on how fast you want your cash; and how much you want to pay for the transaction.
The cheapest way is an online brokerage where you can sell stock for $10 to $20 for the transaction. (someone like E-Trade). You probably will not be able to sell the stock until they have the certificate in hand, (mailed to them, and signed.)
The quickest way is to walk into a brokerage in your town with the certificate and sell that day. You will get a check mailed to you within a week. This is also the most expensive way, (can cost you $100-$200+, depending on the per share value of the stock.)
If there are any Discount Brokerage offices near you walk into one of those for a lower transaction fee, (usually less than $100) should be quick to get a check, about a week.
Check with banks in your area, some of them have discount brokerages.