To edit a line first select it.
When a line is selected you will see 2 manipulator points, one at the start of the end and another at the end of the line.
A selected line showing the manipulator points at both ends
To move a line keeping its angle to the horizontal constant, left-click anywhere on the line other than on either of the end manipulators and drag the line to its new position. If snap is enabled then the line will move in steps as defined by the grid; in this case the end points may not snap to the grid. To snap the end points to the grid, drag the end points individually.
As you drag the end points they may snap to other objects if snap to objects is enabled.
If you have any point, horizontal or vertical guides on your schematic or PCB and snap to guides is enabled, then the end points will snap to them if they are close enough.
You can also set the lines parameters using its properties panel.
Line Properties Dialog
You can also edit the parameters of the line using its properties panel as shown below. To view the properties panel first select it. Then right-click on it, then select Properties Panel from the context menu that opens.
Click the button to show this help topic.
This is the start point of the line.
This is the end point of the line.
Use this to set the layer on which the line lies. This only applies to PCBs.
Check this box to prevent its properties from being altered or the line being moved.
Here you can set the style of the line.
This includes the:
•The start and end caps
•The lines color.