Network Manager supports Roaming mode. and allows to connect to any available wireless network in range.
1. Taskbar > click Network Manager
2. Select wireless network from the available list
3. Type the network key
4. And now connect

OR

1. Select the connection and press Properties.
2. From network name drop down box select the router. If it is not shown then manually type the ESSID
3. Select pass and type the correct one
4. If ISP provides a static IP then select static IP from the configuration box
5. If the router assigns IP addresses then leave the Configuration as Automatic Configuration / DHCP and click OK