Ok, if you are not using the 501 to act as a DHCP server then you'll need to take this feature out.
In configuration mode:
clear dhcpd
save with: write mem
Now you'll be able to change the inside interface IP address i.e.
In configuration mode:
no ip address inside 192.168.1.1
ip address inside 10.10.0.200 255.255.255.0
Again - save with: write mem
Hope this helps and please rate posts.