New beamer theme installation into MikTeX environment is not too difficult.
Simply, you can install with 2 steps: file download&localization and update tex database.
1. File download and localization
Beamer theme .sty files have different types. We should copy the .sty files of a theme to corresponding sub-directories under the $(MIKTEX_ROOT)\tex\latex\beamer\base\themes\ directory. Have a look inside the sub-directories, all file have corresponding name to their types. For example, beamercolorthemealbatross.sty is in the color directory while beamerfontthemeserif.sty is in the font directory.
2. TeX database update
Run MikTeX’s setting and push a button of General->Refresh FNDB. Then, MikTeX automatically adds the .sty files into its database.