You have a couple of options for taking a L2 or L3 test (L3 is as high as it goes at this point, the tests for L4 and L5 haven't even been written yet) The first option is to find a premier event such as Yugioh Nationals, SJC, GenCon, etc. where UDE is offering judge testing. They always have judge testing at all of those except the SJCs in which they do on occasion. Your second option is to hook find the closest person in your area who is certified to give the L2 or L3 test. Usually you'll find these people working with / for a PTO. Many of those same people (but not all) ill require you to "test judge" at an event or two before giving you the written test to find out how you perform in real scenarios, how you interact with people, how responsable you are, how reliable you are, and how you handle pressure situations.
I encourage you to keep improving your knowledge, congradulations on passing your L1. A word of caution though, the L2 and L3 tests raise the bar considerably. The L2 test usualy takes between an hour to two hours to take. Chances are if it takes you less than an hour you'd best go back and check you answers. It would be wise to have a good deal of floor time judging, judge a couple of major events, and do your homework concerning mechanics and chaining as well as standby and end phase card effects and their resolutions before venturing to take the L2 test.
Best of luck to you! Please let us know how we can help you to achieve your goal.