Remove the black plactic liner panel from the passenger side footwell:

• Remove torx fasteners along the front edge (4 I think)
• Remove two wing nuts on the firewall
• Set the panel out of the way.

Removing the black plastic liner panel will reveal several pneumatic (air) lines taped up there, and a cluster of multi-wire harness connectors. That's the bottom of the ECM.

Remove the ECM:

1. Peel back the carpeting to give you a little more clearance.
2. Each harness connector has blue (I think it is) latches, you have to squeeze them together and pull each of the connectors out.
3. Standing on your head often helps! Look slightly upwards and you'll find a plastic molded bracket attached to the ECM case. Look closer and you'll see I think it's one fastener, "torx" type. Remove that fastener
4. Tug the ECM down out of it's slot. Mine is a really tough pull, it's really snug in there! Mean time stretch the air lines to one side to allow the ECM to pass.

Reverse these steps to reinstall.

There's a small (1-1/2" by 5") cover on one end of the ECM case secured with two hex head screws. Removing that cover exposes the PROM.

Thanks to Greg Ross, member of the Reatta forums, for this information.