If you are just running motors it probably doesn't matter and a lot of other equipment can be jumpered t0 run 208 or 240.
Like John says, this is a PoCo option. They will need to add another transformer, probably replacing the small one you have too.
The typical center tapped delta uses a smaller transformer for the wild leg and they only use 2, leaving one side of the delta open (AKA Delta Vee)
Expect a fee for this.
I bet your transformers look like this.