To Trim or Extend Line Segments
To trim or extend segments, hold down the CTRL key and drag the endpoint of the entity to the required location.
You can also trim or extend entities using the buttons on the Design tab:
• Click 
Make Corner and select two nontangent line segments to trim or extend to create a corner.
Make Corner and select two nontangent line segments to trim or extend to create a corner.• Click 
Trim Segment and select a line segment to delete.
Trim Segment and select a line segment to delete.