Vim 7.4 isn't in the standard yum repo. Compiling and installing from source is pretty trivial:
wget ftp://ftp.vim.org/pub/vim/unix/vim-7.4.tar.bz2
tar xvjf vim-7.4.tar.bz2
cd vim74/
yum install ncurses-devel gcc -y
./configure
make test
make
make install
/usr/local/bin/vim --version