Horn Transpositions

So I started working on a Double Horn Concerto in C Major, I am doing this piece influenced by classical music; but I want to make my 2 solo horns in the key of C major, but they always are a Horn in F. I want to make it so it shows Horn in C and plays in the key of C Major.
This has probably asked before but I cant a find a forum about this specific topic.

Thanks to anyone who responds to this post.

-Stickymm-