To combine two or more process levels into a new single one, do the following:
Select process levels in the flow chart (hold the Shift key down while clicking the desired process levels)
Right-click any of them to open the pop-up menu..
Select Combine subprocesses horizontally/vertically according to way you want to combine them. A new subprocess is created containing the contents of all selected subprocesses and they are aligned according to the way you selected.