You will have to select the video object and then find the speed setting in the mediapool under the "Effects" tab => "Video effects" section => "Speed" sub section. You can change the playback speed here, but also reverse the playback direction. If you want to go below/above the limitations of 0.5 to 2 times speed or reverse the playback direction, make sure the video is not grouped with an audio track. Imported video footage that does have an audio track will usually be grouped by default. You can ungroup objects in the arranger (broken chain icon or keyboard shortcut CTRL+M).