Step 1: Right-click the network icon in the system tray at the bottom-right corner of your screen, then click the Open Network and Sharing Center option. If you can not find this icon, you can also access the Network and Sharing Center menu from the Control Panel on your Start menu. You can also read this article to learn about ways to quickly access programs and menus in Windows 7.
Step 2: Click the Manage wireless networks link in the column at the left side of the window.
Step 3: Double-click the wireless network for which you wish to change the wireless security key.
Step 4: Click the Security tab at the top of the window.
Step 5: Click inside the field to the right of Network security key, then enter the current correct wireless network security key. If necessary, you can also change the Security type and Encryption type from the drop-down menus on this window as well.
Step 6: Click the OK button at the bottom of the window to save and apply your changes.