Again, another dumping ground for neat ways to work with Vim.
To change two vertically split windows to horizonally split
Ctrl-w t Ctrl-w K
Horizontally to vertically:
Ctrl-w t Ctrl-w H
If you have them split vertically C-w J to move one to the bottom
If you have them split horizontally C-w L to move one to the right
To rotate in a ‘column’ or ‘row’ of split windows, C-w C-r