I did mine when I did the head gaskets. I bought a new one from Saturn. First, I removed the old one by reaching under the dash with a wrench and unscrewing it from the back of the tach. Then I fed it out through the firewall. I then unscrewed it from the 90° gearbox adapter on the front of the timing cover.
Installation was the reverse.
Lube it with something like a dry graphite lube before installing.
Reaching the connector on the timing cover is fun. A shorty open end wrench is helpful, if you have one large enough. I did it from the driver's side.