If the appliance was truly a gas fireplace to begin with you can not convert it. There are non-vented gas fireplaces - I assume it is not that. A vented gas fireplace is created to fit in a competitive price niche; so the body of the fireplace is built to take the non-radiant flame produced by gas. Wood makes the surround much hotter through radiation of hot coals - a gas fireplace usually has no coals.
The venting system that goes through to the roof for a gas fireplace is usually B-vent, an aluminum inner, galvanized outer double-wall thin-construct metal chimney. Wood fireplaces are built with all-fuel metal chimney, usually stainless-steel lined. Even these metals are not enough if coal is to be burned in the fireplace, that requires triple-wall special chimney.
So, if the fireplace was originally a heavy-metal and brick chimney fireplace for wood, you can possibly use it for wood, after the fire marshall checks it out. If the original was really meant for gas, it should be rebuilt specifically for the purpose of burning wood.