Your student can take the psat, SAT and ACT anytime, but the PSAT counts for the merit scholarship in 11th ( I think lol)
You will need to call your local high school to register for the PSAT, but for the ACT and SAT you register online and they will give you a list of available schools that are offering the test.
If your town has private schools, they might be test sites and you can register via act/sat web site for those sites.
If you are thinking of AP, you will need to call the collegeboard(where you register for SAT) and get your local AP cooridinators contact information.