on a 2005+ Mustang? Not too hard.
You'll need:
Rent/Buy External Spring Compressor (~$40 Autozone/Kragens to Rent)
New Strut Mounts
Torque Wrench (capable of 150ft/lbs)
Hand tools (ie 1/2" drive with metric set, 3/8" drive...)
When I changed out my upper strut mounts for some J&M Camber Plates I believe it was a matter of taking off 8 attatchments: 2 at the knuckle (connecting spindle to strut), 4 for the strut-mount-to-body screws, 1 for the brake line on the strut, and 1 for the sway bar link. Once the knuckle bolts are removed you just support the spindle with some blocks, and then it's just a matter of removing the strut-mount-to-body screws and dropping the strut out.
Once out, use the spring compressor to compress the spring enough to take tension off the upper strut mount. Then you removed the piston nut on top of the strut mount, replace the strut mount, and put everything back together.
Here's a link to show you how to put camber plates on (same idea). Use the torques provided:
http://www.americanmuscle.com/jm-4bolt-caster-camber-plate-05-09-install.html
Have fun!