How to change 16th notes to 8th notes globally while keeping playback speed (MIDI)?

Hello everybody.
I recorded a MIDI-track playing only sixteenth notes in a 5/16 signature, tempo 60 bpm (quarter notes).
I now would like to change the previously recorded material globally into a 5/8 signature while keeping the former playback speed, so that just the sixteenth notes become eight notes in the editors but the musical tempo stays the same when I hit play.
Is there a way to get this or do I need to re-record the complete track using a new 5/8-signature?

Thanks for any advice (and sorry, if this is an obvious operation which I did not find in the manuals/forum)!

Have you tried to use the Time Stretch tool to double the length of your parts?

No, … never needed it before. Thank you! That fixed my problem. How easy things can be.