Help w/ changing ABS module on '03 windstar

I have an '03 windstar w/ the ABS & brake light on most of the time. This has been going on for quite sometime. After checking for leaks brake sensors these are not the problem. From what other people in this forum have said it sounds like the ABS module, can anyone give me info on how to change this out & how hard it is to do this.
Thanks for any help, Jeff