First, check to see if you need it. Press 3 during boot up and see what CPU version you have. If the CPU version doesn't say CPU v1.3
you can send it in.
YOU can only upgrade the DSP if it's not the current version which by now is in the small minority of units (only those made in the first 4 months or so of production).
The CPU must be upgraded (actually, replaced) at the factory (Ft. Worth).