The new heated printbed will require that you reflash your Series 1 Rumba board with this firmware : this firmware (click to download).
Once you download this .zip file, you'll need to unzip it to your hard drive to use it. Note the location where you unzipped the file.
You will need to download and install the Arduino IDE from here : https://www.arduino.cc/en/Main/Software
Open the firmware file you downloaded earlier by navigating to the folder where you unzipped it. You'll be opening the Marlin.ino file.
You'll need to verify the following settings :
Board : Mega 2560
Speed : 230400
Port : (your COM port)
The Rumba is located under the Series 1 E-tray cover. Before removing the cover, power off and unplug your Series 1 from its power source. The Rumba is the white board in the center near the power supply. Here is a picture of the Rumba : http://www.reprap.org/wiki/File:RRD-RUMBA.JPG
The Series 1 must be powered off and unplugged during the firmware upgrade procedure. You will need to move a jumper to allow the Rumba to be powered over USB. Move the Jumper marked StandAlone over to the pins for USB Powered.
You will need a Mini-USB cable to connect between your computer and the Rumba - You can use the Mini-USB cable from inside the e-tray in a pinch. The Mini-USB port is on the front of the Rumba in the E-tray. Once the USB Powered jumper is in place, the the Rumba should power up when you use the Mini-USB cable to connect the Rumba to your computer. You should see one blue light and two orange flashing lights. [Pictures are coming soon, please e-mail email@example.com if you need pictures now].
Once this is all set up, press the Upload button (arrow pointing right) in the Arduino software to upload the firmware to the Rumba. Watch the output window at the bottom of the Arduino IDE for errors. Depending on your old firmware, you may need to flip the motor wires on the Rumba 180 degrees so the colors are running in the opposite direction. This just switches the direction the motors turn in. If you notice to motors moving in the wrong direction, flip the wires. Make a note of any errors.
Let us know if you run into any issues.