Lock wifi so anyone that wants to use it needs a password

Wrong or corrupt file. Try downloading the firmware file again.

You need to download the user guide to get the full instructions from here. The quick guide and datasheet are no good.
TRENDnet Support
Briefly
1. Log into your router management page.
2. Click on Wireless, and click on Security.
3. Click on the Authentication Type drop-down list to select your wireless security type.
you have a choice of WEP,WPA, WPA-Auto, or WPA2 . WPA2 being the most secure. The user guide gives full details of each setup.

You have to look on the tag at the base or back and find the IP address and admin / password sign in to set it up. Set of numbers like 192.168.0.1 or www.routerlogin.net then when on the routers server you can enter your ISP details to get the router setup.

Set it in the router and don't give it out to anyone who could share it with someone else. A way of giving it out at all, is entering it yourself to others devices.

There is a good page at the link I'll show below that tells about default addresses and login names/passwords for Trendnet routers. Although 192.168.10.1 is -common- with Trendnet, so is 192.168.1.1 - and if both of those fail, find the little reset button near where your LAN/Internet source line plugs in, with a small object (unfolded paper clip will do) press and hold the recessed reset button for several seconds, then power it up as normal. This resets the router back to factory defaults.
router defaults com

Normally on the back of a router there is a reset button that will set the router back to the way it was when you first removed it from the box. Hold this button with a pin or tip of a pencil for 10 seconds and then go through the original setup process you went through. This is where you can setup your wireless password and your router password as well.
Check out the Trendnet web site for more detailed instructions if you do not remember.
Good Luck.

I have forgorren my user and password of my trendnet tew-424ub router after a long time of not using them. Can anyone help me recall or maybe just reset them, so I can addess tyhe router page again?

What password are you referring to; Wireless Security or Web password to access the Router's interface?

If it's the 2nd; Open http://192.168.0.1 (default IP) on your web browser, type username: admin and Password: password. Click on Password then change the default password.

If it's the 1st; Open http://192.168.0.1 (default IP) on your web browser, type username: admin and Password: password (put you correct password if you change the default password).. Click Wireless on the left, Enable Encryption WEP or WPA; for WEP 64 bit you will have to use 10 HEX, meaning 0-9, A-F (e.g. common is phone number). If WPA; password can be set from 8-64 characters long.

Angel .

You need to set up wireless network first. Follow router instructions.