No you can't, but I'll just copy+paste what it says in there.
most of the levels are put into a .rar file to upload onto a file
sharing site, you should download WinRAR before trying to download any
of the levels.
Download Here: m http://www.win-rar.com/index.php?id=160&dl=wrar371.exe
1. Put the .b3d file in the custom levels-->level data folder
2. Make a folder in the custom levels folder and name it Textures
3. Put any pictures that are downloaded with the level into the textures folder
may not show up... if you really want them-like for the 4frnt night
shoot level or the Jibbit level, you can replace one of the main levels
in the main folder and put the texture files in the main folder. I hope
I explained that well enough)
Hint: read the "How to install" document