How to see top processes sorted by actual memory usage?

use quick tip using top command in linux/unix

$ top

and then hit Shift+m (i.e. write a capital M).

From man top

SORTING of task window
  For compatibility, this top supports most of the former top sort keys.
  Since this is primarily a service to former top users, these commands do
  not appear on any help screen.
    command   sorted-field                  supported
      A         start time (non-display)      No
      M         %MEM                          Yes
      N         PID                           Yes
      P         %CPU                          Yes
      T         TIME+                         Yes

Or alternatively: hit Shift + f , then choose the display to order by memory usage by hitting key n then press Enter. You will see active process ordered by memory usage