Zoom in to make the transition visible(and make sure the track is expanded so you can see the cut point and the transition).
Using the Rolling Edit Tool (located on the tool bar), you can drag the cut point left and right, and the transition will follow. This allows you to drag the transition, while at the same time changing the out point of clip A, and the in point of clip B.
You can also drag the left and right(starting and ending) of the transition, on the timeline. This allows you to adjust the length of the transition without changing the cut point. Use the (default) select tool for this.
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