Unfortunately, if you're using a Linux server odds are pretty good you can't do it yourself.  You'll need to ask your host to do it for you.   It's a free program so hopefully your host won't have a problem with it.

Of course if you're running a dedicated server or a VPS where you can install your own program you can go to the ImageMagick site and download the binaries for your Linux distrubution.  If there isn't a binary package for your distro you can also download the source and compile it yourself.

If you're running on a Windows server you may be able to get the Windows package from the ImageMagick site and use it.  Although I've personally never installed the Windows version so I can't be certain it works.