1. See if this youtube or links on the right will help.

http://www.youtube.com/watch?v=rbvxHYFBX2c

2. Please post a Pic of your trimmer's head.

3. I'm not getting your model specifically but here is another link.

http://www.ehow.com/how_7797468_string-john-deere-string-trimmer.html

I believe yours is a Homelite BC1600 (UT-15198), private labeled for John Deere. There should be a threaded knob on the end of the string head, which has a left-hand thread. Turn left to tighten and turn right to loosen. Spin it all the way out, and then the string spool should pull straight out.

Do a Google search on BC1600 or UT-15198 and see if the exploded diagram for the trimmer head looks correct.

Check it out: http://weedeaterguides.com/re-spooling-a-weed-eater-when-to-do-it/.

you can refer this http://weedeaterguides.com/category/weed-eaters-blog/ to find the answer for your situation..