Click on setup. Select Speaker Configuration, then select Bass Management. Under that you will see the configuration - Movie, then under that you see your connected speakers, depending on your speaker setup..
Example : Front - Small 80hz
Center - Small 80hz
surround Small 80hz
Aux Small 80hz
You can click on the individual speaker here and select the size. Look at page 15 of your user manual. Note. The subwoofer cannot be adjusted here, as the Anthem Arc controls its settings, crossovers filters, levels, etc. Do you have ARC (Anthem Room Correction enabled? As you have a new Subwoofer you or your Installer will have to run the ARC Calibration again. The new Subwoofer will have totally new characteristics than your previous one and will measure and interact in your room differently.
I am only on my "Trainer Wheels" myself in regard to the Anthem MRX700. There is a lot of excellent information in the Anthem MRX 300, 500, 700 tweaking guide. It is currently located on Page 2 of this section of the Forum.