Using Toolbox
First download the latest build here
Right click the zip and go to properties.
Check the "Unblock" option
Then click "Apply" and "OK"
Lastly, you need these 2 required installs
These are required for most texture viewing as it is the main library to decompress/compress these back.
Now open Toolbox.exe.
You can now use the tool. File - Open to open new files. Files can also be dragged/dropped to the tool. The green arrow is for automatic updates.
Note the date on the toolbar is not up to date. The latest is always up on the releases, though the date does not change unless the updater is used!