With the proper tools/materials and knowledge (obtained in various sources online in print and video form)...it isn't rocket science to swap out the handguards. It all comes down to what you are comfortable with doing, and if you don't have the tools, whether you want to invest the money in them if this is the only time you'll be swapping out handguards or doing any future AR builds down the line. Sometimes, if its an isolated project...it is more cost effective to just have someone else do it for you (even if you have to pay S&H both way to get it into the hands of a good smith). Totally your call since its your money and rifle.
To give you an idea...you'll need an adjustable, ft/lb torque wrench (1/2" or 3/8" drive...usable range of 40-90 ft/lbs), barrel nut wrench for removing the stock DPMS nut (the Lite rail comes with the DD rail to install their proprietary bbl nut), upper receiver vise blocks to secure it properly in a bench vise (plus you'll need the bench vise obviously), a quality anti-seize compound (Aeroshell 33MS is my preference and is the mil-spec required compound for barrel installs), in/lb torque wrench to remove/reinstall your gas block (assuming its a screw model and not a pinned model), possibly a strap wrench to assist in removing the DPMS tube (again...depending on which one it is, you may or may not need it), etc., etc., etc. Now...that's going "by the book" and you can certainly cut corners if you so choose, but to do it properly...you need the right tools for the job.
As for compatibility, just make sure that you order the appropriate DD model to match your platform (i.e. - they make multiple barrel nuts for basically the same rail. You'll need to ensure you get the DPMS nut and NOT the RRA or Armalite nuts). Also, depending on which particular receiver height you have from DPMS, the handguard rail may or may not line up properly. Current production rails from DD and current production rifles should be fine except for those like the Sportical, 308B, 308T, etc. If you look at the rifle and it has a higher than typical receiver rail...the DD 7.62 Lite rail won't work (or at least won't align to give you a same-plane top rail).
