To install this package, run in Emacs:
M-x package-install RET windresize RET
This mode lets you edit the window configuration interactively just by using the keyboard. To use it, type M-x windresize; this puts Emacs in a state where the up/down and left/right arrow keys resize the window dimensions. To return Emacs to its ordinary state, type RET. See the docstring of `windresize' for a detailed description of the other commands that are available while windresize is active.