That's fairly simple: Download
miktex-biber-bin.tar.lzma from a CTAN repository (direct linked to a mirror near you) and extract the files anywhere on your computer (two steps under Windows). You get a ‘texmf’ directory containing 3 subdirectories (doc, miktex and tpm). You just have to put these 3 subdirectories under the root of your LocalTeXMF directory, and to refresh the FNDB via MiKTeX Options (‘Settings (Admin)’).
If you do not have a LocalTeXMF directory, create one first and declare it via MiKTeX Options, ‘Root’ tab, see Create a local texmf tree in MiKTeX.
Added on 09/20/2015:
MiKTeX 64 bits repositories finally got this summer a
miktex-bin-biber-x64.tar.lzma file, so there is no need to make a manual installation of the 32-bit version any more: just do it through MiKTeX Package Manager if MiKTeX is already installed. For a first installation, I guess MiKTeX basic installer does it automatically.