See [this fandom article](https://vim.fandom.com/wiki/Resize_splits_more_quickly). Summary
```vim
; change height
:resize 60
; increments
:res +3.5
:res 4

; vertical splits
:vertical resize 80
:vert res +5
:vertical resize -5

C-w + / C-w - ; resize horizontal split by one row
C-w < / C-W > ; resize vertical split by one row

C-w =         ; resize all windows to equal dimensions
C-w _         ; resize window to max height
C-w |         ; resize window to max width
```