I'm not sure about downloading it, but after downloading it you'd have a DLL file probably called the same as the Plugin you're trying to download.

Copy & Paste this DLL to: C:\Program Files (x86)\Image-Line\FL Studio 11\Plugins\VST\
If you use a 32bits OS, ignore the '(x86)'.


After that, inside FL, go to Channels>Add One>More...
Click Refresh in the window that pops up > Fast Scan > Under VST 1 & 2 Plugins a red name'll show up, flag it and exit.

If it's a VST Effect, go to the mixer > Random channel > Select > More...


Hope this helps!