Contact psychologists in your area to inquire about IQ testing. The Mensa IQ test is one that needs to be administered by a psychologist. There should be a psychologist near you who can provide it.
Visit nearby schools, colleges and learning centers and ask if they administer IQ tests. There are many different tests and there is not a set standard for them, so you may do very well on one and not as well on another.
Go online and take IQ tests on the web. There are multiple websites that provide IQ testing free of charge. The quality of the tests can vary greatly so take several to come up with a general range of scores. But remember, don't take the results too seriously.