There are traps you can buy for the yard that kills them, but it's probably best to call an exterminator.
Call an exterminater asap.
You need a professional licensed exterminator. They get into nooks and crannies you can't get to. Call and get bids asap! Here is how to hire:
The most effective way is to hire a professional from a company such as Orkin. There are other ways you can try on your own though such as the ones in the article below. My concern about doing it yourself is that termites live and eat mostly in places where you can’t see them. This means that you won’t be able to see if your control method is really working.
Have your exterminator advise of trouble area's. They should to this as part of the treatment. Drainage is important as you don't want any standing water next to foundation. Don't put mulch up to foundation, rake it back about 12 inches to create a dry dirt area, then spray grass killer on it as needed. Be sure you are using downspout extenders, and channel water form AC unit drip lines away from foundation also. Keep in mind roof leaks. A roof/chimney leak, which you may not notice, can travel from roof to ground, creating a path for termites all the way up. If present, your exterminator should notice this.