remove the entire frame and buy a new pre hung door and one that is steel skined with insulation in the middle. Hang this door, it will come with a metal threshold also and two pre drilled holes for the handle and a dead bolt. They will run about $150 at a home center. If you have NEVER done this, I would let a handyman do this. A small mess up on the door will be a lifetime of frustration. Squareness is the key and you have to make the kit square even if the hole is not.
This door is a six panel door, wood sim grained already primed, metal threshold, with metal jambs, you will want a door that swings IN with hinges on the right and threshold on the outside. You might have to build up the area supporting the threshold, use a pressure treated 2x4 for this.
The jamb of the old door would not hold any weight if this happened.