Use Crop to Selection 
to decrease the size of the picture by removing the parts that are not wanted. Use one of the selection tools, e.g. Box Select 
or Freehand Select 
, to select the area of the picture that you wish to keep, then in the Canvas drop-down menu, select Crop to Selection 
. The parts of the picture outside the selection box are removed and the display adjusts to show the remaining part of the picture at the largest possible magnification.
Crop to Selection is unavailable if there is no selection. Crop to Selection only removes rectangular areas of the picture, therefore the results will be the same whether you select the area using Box Select 
or Freehand Select 
.
Shortcuts
-
Paint Window Control Panel, Edit:
-
Keys: Alt, D, P