MN-700 can't find MTU settings

I need to set the MTU size to 1500 for my wife to be able
to use vpn over the wireless connection. How do I do this
on the MN-700?

It's already done. Depending on whether you use PPPoE or Static/DHCP.
PPPoE uses 1492 while Static/DHCP uses 1500.
There's nothing you can do to change this, it's a standard.
If you need confirmation, please check here:
http://www.dslreports.com/faq/5793

c4s wrote:
> I need to set the MTU size to 1500 for my wife to be able
> to use vpn over the wireless connection. How do I do this
> on the MN-700?