I've been struggled trying to install the
unicode-math package manually since I don't know if there is another way to accomplish it.
So I downloaded the entire package from CTAN.
And I followed the instructions given in this post.
But after doing it and compiling a TeX archive with XeLaTeX, It stills giving the same error and LaTeX indicates that the .sty file is not installed.
So any help is appreciated.
PS. I'm using TexMaker as my TeX editor.