You will not be able to wirelessly extend the range with your ABS. First of all, only AEBSes can do that, and secondly, they can only extend from 1 AEBS to another AEBS (no brand mixing). You could run a long ethernet cable to the ABS, and disable DHCP serving, but that may not be feasible for you.
You may want to compare signal strength of the two. You only need 1 really, so stick with the one that works best.
To config the router, log into its IP address (you'll need the default user name and password, which you WILL want to change). This is probably listed in the docs somewhere. Most likely it is .1 on your subnet. So, if you Mac is 192.168.0.2, then the router would be 192.168.0.1. You should be able to make any and all config changes once logged in. I wish A(E)BSes config'ed this way...