Vim Window Commands have ex alternatives.

For example <C-w>o closes all other windows and keeps the current one. But you can do the same with :only

This is awesome and you can use the :help to find others.

However things like <C-w>J/K/L/M etc don't have such commands, what then? Well, that's where :wincmd comes in. It is the equivalent to <C-w> so you can use it instead so try :wincmd J or any of the other <C-w> commands...