The easiest way to remove all settings from an interface is to use the default interface configuration command. For example, if you've configured Frame Relay interface with subinterfaces ...
interface Serial0/0/0... and have erase all interface-specific configuration, the ...
no ip address
interface Serial0/0/0.100 point-to-point
ip address 172.16.1.1 255.255.255.252
ip load-sharing per-packet
ip ospf cost 50
frame-relay interface-dlci 100
... gets you there. As you can see, after the configuration change, the main interface has no IP address and the subinterface is deleted.
rtr(config)#default interface serial 0/0/0
Interface Serial0/0/0 set to default configuration
a1#show ip interfaces brief
Interface IP-Address OK? Method Status Protocol
... non-relevant lines deleted ...
Serial0/0/0 unassigned YES TFTP up up
Serial0/0/0.100 unassigned YES manual deleted down