`:vsplit` (short form: `:vs`) split the Vim viewport vertically. `:30vs` splits the viewport, making the new window 30 characters wide. Once this 30 char window is created, how would one change it's size to 31 or 29?

With horizontal windows `Ctrl`-`W` `+` increases the number of lines by one. What is the equivalent command to increase the columns by one?