Where can I change my MMS settings on my Verizon HTC 8x?

[Windows Central Question]

I bought the phone off e-bay earlier this year and was able to configure both the APN and MMS settings manually to get to work on the Bell network in Canada. Now that I an switching to another Canadian network, I can no longer find the MMS settings option. I know it was there before, but now it's gone, Suggestions anyone?