Grabbing vertices of motion tracker

Hi folks. I’ve recently downloaded Blender 2.69 to do some motion tracking on a video recording. While playing around with a video, I noticed that the marker vertices weren’t always where they should be. Specifically, one of the vertices has wandered off a little. I would like to correct it manually. How would I go about moving that vertex? The delinquent vertex can be seen in the top left-hand corner of the frame in this screenshot:

PS: Blender has come a long way since I used it the last time six or seven years ago. Wow!

Select the marker at the appropriate frame, and drag it back to the right place.

Hi David, thank you! I had attempted this myself, however there must have been a hitch in the mouse preferences on account of me using a laptop. It works now!