2704n router setting to fix internal ip addresses

[#1]

We have a 2704n router. Each time it turns on, it gives a different ip address to the wireless printer (HP Officejet 6500a e710n-z). I have to look up the IP address in the printer’s wireless settings, then  change the setting on each PC on the network. I’ve tried telling the printer to use the same IP address each time, but the router seems to give it a different address.

How do I fix the IP address in the router?

[#2]

This might answer your question.  There is a hidden expert user web admin page:

https://community.plus.net/t5/Broadband/reserve-ip-address-range-on-2704N-router/td-p/1291809

[#3]

Thanks for your reply. Sorry to be so dim, I need this stuff spelled out for me. 

Do I need to define static IP addresses in the LAN page?  :

DHCP Static IP Lease
Enter the Mac address and Static IP address then click "Apply/Save" .
MAC address please according to the format "11:22:33:AA:BB:CC".

Or do I disable something?