Obliterate the warranty deed by defacing it and tearing it into small pieces. If the document has been destroyed before it can be taken by someone for filing in the county office for recording property transfers, your ownership in the property will not have been conveyed.
Communicate to the grantee of the warranty deed--the new owner of your property--that you regret conveying the property and want to reverse the transaction. If the grantee is a relative or friend, you might be able to work out the situation and have the property reconveyed back to you. Use the same form of warranty deed to perform the reconveyance so that the same ownership interest in the property is once again yours. If you conveyed the property by warranty deed as part of a sale to someone you did not know prior to the sale, it is highly unlikely that you'll receive the type of cooperation you are looking for.
Consult with an attorney experienced in real estate law in your local area and explain to him the reasons why you want to reverse the warranty deed, if you find the grantee uncooperative. In the event that the conveyance of the property involved any facts indicating that you signed the warranty deed by coercion, fraud or duress, you may have a valid legal reason to reverse the warranty deed. Your attorney should be able to advise you on the procedure in your state for reversing a warranty deed for any of the foregoing reasons. In most states, the procedure will involve filing a "quiet title" lawsuit in which you will request the court to make a judgment invalidating the warranty deed you signed.