Place the record between two sheets of stiff, flat cardboard and store it on edge, tightly packed between other records or books on a shelf. Be sure the whole surface of the record is under pressure from both sides. Leave it alone for two months. The warps should have pressed out the next time you check. Always store vinyl records the same way; they tend to warp when laid horizontally, or to sag when stored too loosely.
Place the record between two sheets of nonstick metal. Apply the iron gently, on the lowest setting, for three minutes. The warmth may release any remaining warps. Let the record cool and store it in its sleeve as described in Step 1.
Place the record between two pieces of smooth, flat glass if none of the other methods has worked. Place this arrangement on a flat spot in the sun for two hours, or in an oven heated to 150 degrees Fahrenheit for 10 minutes. Let cool. This step is a last resort, as it may permanently damage the record.
Pack boxed records tightly between sheets of flat, stiff cardboard until no more room remains in the box. Store the box on edge.
Purchase an electronic record-straightening machine, which operates on a similar principle to the methods described above, but which can deliver more exact conditions of pressure and controlled heat. These machines are expensive, but if you have a whole record collection or some irreplaceable favorites to straighten, it may be worth the investment to you.