Not sure I have completely grasped what you are trying to achieve there… do you actually want to change what is already being heard there (doubling or halving its speed), or just have the tempo double(or halve?) without what you hear changing?
Anyways, in either case, the first thing you need to do (according to your screenshot), is, in the Transport Bar, change the tempo from “Fixed” to “Track”, then enter the correct starting tempo (87.5 BPM?) in the tempo track Editor window (or create a Tempo track in your project window, and do it there )
What happens next depends on what you wish to achieve …
If you don’t want to change what is being heard, but simply set a double tempo against it (e.g. for overdubbing at the new tempo), is change all tracks from Musical Timebase to Linear Timebase (for each track, change the yellow “quarter-note” icon in the Inspectorinto a “clock” icon)… and make sure that, in the Audio Pool (if necessary) all audio clips do not have Musical Mode checkmarked.
You can now enter new tempo events at the appropriate places in the Tempo track.
If you do want to change what is already being heard, I think I need a bit more detailed info… don’t want to set you running off in a wrong direction .