You must use a special tool that has two rails that slide o each side of the ECU. That tool can be rented for a $75 deposit (refundable upon return of the tool) from IPD or you can pay a tech from a Volvo Retailer to do it for you. If your car has an automatic transmission, you will have two ECUs. The one closest to the engine is the auto tranny ECU; do not remove that one. If you were driving the car, wait 5 minutes (after you turn it off and with the key off the ignition) before removing the ECU. And make sure that you do not turn on the ignition while the ECU is unplugged; you can cause major damage to the car.
Are you upgrading it? If yes, who are you going with?
Yannis