See this fandom article. Summary
; 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