Before removing the ECU, disconnect the battery or pull the "Trionic" fuse
Move the carpeting away.
Unlock ECU harness by pulling the lever and unplug it. Undo a screw
in the lower right corner. The ECU slides down.
The new ECU plugs right in. After the installation, perform an
adaptation run by doing a series
of full throttle accelerations in high gear from 2000 to 4500 RPM.
It helps if you can find a long road going uphill.