I just recently did this. Assuming your fireplace is in fact safe to burn wood, take 2 small pipe wrenches and disconnect the gas line where it comes into the firebox. Make sure the gas is shut off before you do this!!!!! lol

My 'gas guts' were buried under sand and stuff so after a little cleaning it all came out in one piece. The grate was seperate and Im using that for my wood fires.

Then just cap the gas pipe with the appropriate size cap and thread sealant or install a gas ignitor for wood fires.

Enjoy, hope this helped
Dave