If you insist on TeXStudio you may now download TeXStudio 2.4. You can now set up your xelatex
and lualatex
commands with this version.
I am using Ubuntu 12.04 but TeXStudio 2.4 must have the same features as the Windows version.
See in the picture below that there is already a separate box your xelatex
and lualatex
commands.

Now, in the build
option, choose your default compiler. You may now choose either xelatex
or lualatex
. See picture below.

If you don't want to update just yet, you may look at my comment in this answer.
But it is a hassle to keep on changing your default compiler. Some times it is better to just open cmd
and run xelatex myfile.tex
or lualatex myfile.tex
. Just CD to your source folder before doing the compile.