Summarize:

Remove the nut and washers on each bolt and set them aside for final installation. The flange lip will have channels on either side, into which you can feed the heads of the 2 bolts. Position the bolts so that they are pointing straight up and are directly across from each other. If you’ve lost the new bolts, you can likely reuse the bolts from the old flange, provided that they’re still in good condition. The lip of the flange should rest flush on the floor all the way around, while the neck of the flange should slide snugly into the pipe. Position the flange so that the protruding bolts are at the 3 o’clock and 9 o’clock positions (presuming that the back of the toilet will be at 12 o’clock).  The neck of the flange should have a rubber gasket that creates a seal against the inside of the overflow pipe. If the lip of the flange won’t rest flush to the floor all the way around, the flooring is likely warped or damaged due to water. You should do any needed floor repairs (or call in a pro to do them) before proceeding. Use a screwdriver (turning it clockwise) to secure the screws that came in the product package. There will be pre-cut holes in the flange lip where you should drive the screws in.  Use a drill to create new pilot holes in the flooring, if needed. Existing holes from the previous flange may be in the same location but be too large to hold the new screws. If so, use a mallet to tap plastic wall anchors into the holes, then drive the screws through the flange lip and into the anchors. Most toilet flanges come with 4 screws, but yours may have more or fewer. Pick out any pieces of wax ring, loose screws or washers, etc. before removing the towel or shirt. Otherwise they may fall down the pipe. Don’t plan on using this towel or shirt again—just toss it! Press the rounded side of the wax ring over the pipe stub that surrounds the opening on the bottom of the toilet. Press firmly all the way around the wax ring, but don’t deform it.  Pros usually prefer to apply the wax ring this way in order to guarantee a good seal around the toilet. However, you can also lay the ring (rounded side up) on top of the toilet flange, then set the toilet on top of it.  If you’re using the newer type of “wax ring” that is actually a rubber gasket, lay it rounded side up on the toilet flange and place the toilet on top of it.
Feed the included bolts into the new flange. Push the new flange on and into the outflow pipe. Drive screws through the flange lip and into the flooring. Remove the towel or T-shirt from the outflow pipe. Tilt up the toilet and push the new wax ring into place.