I want to increase the maximum available number of IP addresses that DHCP can allocate, but when I try to go beyond .149 it comes up with an error saying that "PPTP IP and SSL IP" range overlap. We do not need either of these, but I cannot find where I can disable them so that I can extend the range
The Range overlap means same range of IP subnet you had assigned on another interface of the router. So first of all check all other interfaces/VPN configuration Pool for any overlapping the subnet mask.
Regards, Deepak Kumar, Don't forget to vote and accept the solution if this comment will help you!