There are 2 ways to edit a point guide, dragging it or using the Properties panel.
You can hold down the left mouse button on a guide and then drag the mouse to move the guide. You will see the X, Y values of the point change as you move it. Press the 's' key to turn snap on or off.
Point guide's vertical position displayed during dragging
If you select a point guide and the Properties panel is visible, the point guide properties dialog will be shown.
Point guide properties
The X or horizontal position of the point guide.
The Y or vertical position of the point guide
Pressing the button displays this help page.