I’m trying to change the tempo in a project with all midi tracks (no audio). I’ve changed all the tracks to musical mode and activated the tempo track, as I read on other posts. I entered a faster tempo than what I recorded the tracks with. The metronome does click at the new tempo and the cursor moves appropriately faster through the tracks, but the notes are still playing at the slower speed. What do I need to do in order to record the midi at a slow speed but then make it play faster when I increase the tempo?
Strange 
it reads like you’ve done everything correctly.
What instrument(s) are the MIDI tracks routed to?
Do the MIDI Parts still look the same length (as regards bars)?
They are routed to various software instruments (Superior Drummer, Dimension Pro, EastWest Bosendorfer). The length of the midi notes stays the same no matter what I change the tempo to.
The visual length, relative to Cubase’s grid (which is correct)? or the actual length, in terms of what you hear?
Does this happen in all projects, or just in a specific one?
If you can, please upload two small screenshots… a MIDI Part inside the Key Editor, and then the same MIDI Part after having altered Cubase’s tempo track.
Both. They appear the same length in the grid and they sound the same.
In my previous DAW, when I increased a tempo by typing it in, the notes immediately adjusted in length, also automatically adjusted to the correct start times relative to each measure. Everything was still lined up, the metronome still counted out the beats in each measure correctly, it just all went faster. Like when you resize a photo in editing software but keep the ratio intact, so everything still looks in correct perspective, just smaller/larger.
Not to knock Cubase because I’m still a relative newbie, but it was so very easy in the old DAW–type in a new tempo, that’s all you had to do. This has really frustrated me in Cubase. I’m sure I’m missing something simple but have messed with it all afternoon and still can’t figure it out.
Are you sure that you have set the tracks to Musical Timebase? (they should have a button like a “quarter-note” when in Musical Timebase, which changes to a “clock” button when switched to Linear Timebase)
On the Transport, you have Tempo set to Fixed, not Track as needed.
Each track has a ‘lit’ orange musical note button, which hopefully is correct.
It doesn’t make any difference whether the transport is set to track or fixed, the result is the same. Believe me, I’ve tried both, many times this afternoon…
Try a new project. Import a MIDI file, make sure the track’s in Musical Mode, the Transport is set to fixed and adjust tempo via the Transport.