Go into run type:
command then it will open the command prompt then type:
ipconfig and it will show you you're ip, in my case its 192.168.1.101 if you want to access that computer, go to 192.168.1.1 and enter the pass, i think the default is admin, or if you changed it enter it, go to advanced, and click forwarding and click upnp forwarding, now enter the port number that you need to access to connect to the remote computer, on both sides, and enter under the ip address you're results from the commands above, which for example mine is 101 that comes from the ip from the computer u want to access. (101 comes from 192.168.1.101 (you're ip may very))
Whatever service/program you are trying to connect to will have to forward the proper ports for the machine you want to connect to. Do not enable upnp forwarding. Linksys devices allow you to forward specific ports to specific machines. ALso dont DMZ the machine unless you absolutly need too (and you should not). Any further questions can be answered by the manual for the device.