There are 2 ways to edit an angled guide, dragging it or using the Properties panel.
You will see the angled guide in red together with 2 point manipulators. Drag any of them to edit the angled guide.
You can hold down the left mouse button on an angled guide manipulator and drag the mouse to move the guide. Press the 's' key to turn snap on or off.
Dragging an angled guide
Or, you can drag on of the 2 guide manipulators. You will see the angle change as you move it.
Angled guides manipulators
Guide during dragging a manipulator point
If you select an angled guide and the Properties panel is visible, the angled guide properties dialog will be shown.
Angled guide properties
The X or horizontal position of the guides start or end.
The Y or vertical position of the guides start or end.
The angle of the guide in degrees.
Pressing the button displays this help page.