Hello and welcome to Just answer,
The starter is replaced from under the vehicle, if you have the necessary equipment to raise and properly support the front of the vehicle it is not that difficult of a job from there.
Make sure you first step is to disconnect the negative battery cable.
And the last step is to reconnect the negative battery cable.
Below are the instructions for the 3.1 engine which most century's came with.
Important: The starter motor on this vehicle is not serviceable and must be replaced as a complete unit.
Reverse to install
Tighten the starter bolts to 43 N·m (32 lb ft).
Thank you Peter,
Good luck and let me know if you run into anything