The best kit you can buy, and the one that most of us use, is the one that Ben sells at the sister site to this forum www.poolsolutions.com It will measure chlorine levels up to 50. Consider getting it. It is well worth the money and will test for any and everything you need to test for.

In the meantime, you can extend the range of your kit by diluting the sample. Take one part pool water and one part distilled water, mix, test as usual and multiply the result by 2. If you need go higher -- one part pool water, two parts distilled, multiply by 3, etc. Of course, you lose a little accuracy with each dilution, but it is better than nothing and usually better than a pool store will do.

What level you keep your pool's chlorine level at is dependent on your cya reading. See the chart at the following link for more about that.

http://www.poolforum.com/pf2/showthread.php?t=365