Call your water company and ask them where the shutoff is. They should shut it off for you and turn it back on, but that is a pain in the neck and there may be a charge for the service.
You will probably need a special wrench to shut it off. They usually require a 5 sided socket with a long handle and should be able to turn it off with little or no digging. The access is often flush with the ground, sometimes in a metal box. You will probably need to disturb the meter, in which case they will want to install a new seal.
When I replaced mine, which was leaking, it was easier to leave the old valve in, drill and cut the guts out of it to eliminate the flow restriction, and put a new full-port ball valve above it. If you put it after the meter you don't have to involve the water utility.
My water utility wanted about $150 to replace the valve. I bought one at HD for about $15. It will be easiest if you can find one that doesn't require a bunch of new adapters to install it. I was able to put mine between the old one and the meter by just cutting out a piece of tubing where the meter was intalled.
If they give you any flack you can always call dig-safe and tell them you are going to do some grading and digging and need to have the water company mark it out so you don't break their pipe when you dig. They have to do that for free.