I can''t say from experience since mine came with the boat. That said, my guess would be that it is a pretty straightforward job for anyone with the experience of installing or replacing a head, manual or electric. Since you are replacing - the biggest task may be electrical rather than plumbing. You will need a seperate circuit run from the electrical pannel through the included switch and fuse to the electric motor.
The raw water intake and discharge to the holding tank are virtally the same as your manual head. You may want to simplify the job by using the same manufacturer as your current head if you can find one with the same fastenings (bolt pattern).
I''m out on a limb guessing installation time for a job I''ve already admited that I''ve never done myself, but if it is a simple replacement of the plumbing and the run of a new 12V line I''d guess 3-5 Hrs for a professional.