I'm pretty handy and I've replaced interior doors before.

Should I try to do my back door myself? Or should I probably hire someone to do it for me?

I hired it out and got a couple of yahoos, wished I had just done it myself.

Had Home Depot do ours and add an Anderson glass door as well. They did a very good job but was not a real cheap project.

not that hard to do, get the old one out and clean up the threshold area well, use some pl4000 construction adhesive (polypropylene glue) and lay a good bead in a zig zag across it front and back of the threshold area, set the new door in and move back and forth just a little then align in the hole.
I use 2.5" trim screws to set them (almost no head, square drive) and wood shims you buy at lowes/home depot, put one at the top hinge and level the inside jamb on the hinge side, carefully put 2 more in making sure the hinge side stays straight and level (one at each hinge), use the shims to keep it from pulling in. on the strike side put shims at the strike area (latch, knob etc) and look at the gap up and down, making sure it is even all the way and about 1/8", put one screw through the shims to hold them at the strike, go to the upper and do the same, bottom and repeat making sure the 1/8" gap is even all the way.
check for level and square multiple times, one screw can pull it out and mess things up if you are not careful, check for level both in/out and inside the jamb on both sides, hinge side is the critical one.
get it all adjusted and lined up and shim it 2 more times on the strike side, between hinges and put 2 screws through all shims (inside/outside), fill holes with wood dough and let dry, paint.


and there ya go, hops how to set a door in only 37 easy steps.

http://www.ezhangdoor.com/home
I have used these with great success.

Dang Hop! You've done that 3 or 2 times!

One more add in for the OP. If it's a pier and beam home, be aware that the floor might not be perfectly level and you may have to shim the threshold. If you plumb and shim and set the jambs, then later realize you need to lower the hinge side to make it square, you're going to have to start over. Be prepared for your rough opening to not be square if this is an older home, that's what all that free space between the studs/header and the door jamb is for, to square it up. Take your time, and don't forget to plumb it in both planes, if you're not careful you'll have a square door but it will be leaning in or out and want to shut or open on it's own.

It's a slab foundation but thanks for the info.

I think I'll give it a shot myself.

Thanks HOP for the advice.

not as much worry for pier and beam for exterior doors, they usually don't have much of a problem. I watched bob villa once, just once.