Adjust Guifont Size in vIM

function! IncrementFontSize()
  exe "set guifont=".join(split(&guifont)[0:-2], '\ ').'\ '.(split(&guifont)[-1]+1)
endfunction

function! DecrementFontSize()
  exe "set guifont=".join(split(&guifont)[0:-2], '\ ').'\ '.(split(&guifont)[-1]-1)
endfunction

nnoremap <C-Up> :call IncrementFontSize()<CR>
nnoremap <C-Down> :call DecrementFontSize()<CR>