Hi. just follow these steps:
1) Type 192.168.1.1 in your web browser to enter your router.
Note: password/username should be admin
2) Go to wireless section - security
3) Select your wireless security - WEP is the most basic and weakest form of security, but it is easy to setup. I would recommend you to use WPA 2 if available. Set data encryption to AES and then set your Preshared key.
4) Press OK and then you're done!
Click OK on the popup message, confirming the password change. The administrator password for the router has been successfully changed. Hope, you can easily lock your Tenda router.
How to Lock My Wireless Tenda Router?