Replace all spaces with new lines (in the current line only):
Replace "%3A" with ":" and "%2F" with "/"
If substitution consists from more than one step and is used frequently, it is easier to use a hotkey for that. To map the substitution above to the hotkey "-r", add into
let mapleader = "-"
map <Leader>r :s/%3A/\:/g<CR>:s/%2F/\//g<CR>