There are times when you may need to connect to the same wifi network whose password has been changed but wifi network name remains the same, in such case you will need to forget or delete the already remembered network connectivity settings stored in windows.
1. Open start menu, search for manage wireless connections and click to launch it as shown in the image below.
2. Under wireless network management, right click on the network which you want windows to forget or reconnect and then select remove as shown in the image below.
Once you remove a particular network from here, you can reconnect now to that network by entering the new password.