How can I nuke a Mojave partition from Sierra?

[InuNacho]

I wasn't sure where to put this in the Mojave or Sierra section so if its in the wrong place, I apologize.
A while back I installed Mojave on the second drive in my MacBook Pro and now want to reclaim the 80GB I set aside for it. In disk utility all the options to remove the partition are greyed out. How can I go about removing it?

 

[Fishrrman]

Boot from the Sierra drive
Open disk utility
Go to the view menu and choose "show all devices"
Can you now see "the second drive" in du's window?
The "top choice" (representing the physical drive) is the one you need to erase.

 

[Sanddoc]

Sorry I can not help you, As I am in a worse situation then you.
I made the big mistake of installing Mojave over my High Sierra. Soon after I found that
although many things worked fine in Mojave, a few important things did not, like ( light and dark) modes
my menu bar is completly unreadable and side bars come out dark.. Also the system is very slow
and always is searching...
I have a 750g HD, and I have tried a few things to remove the Mojave partition, but to no
avail...
My question to the Forum is this, If I can remove all "added apps, files, movies, music"
to a thumb drive, can I then regain all the empty space with my HS partition?
sorry I am not trying to high jack your post Inu, just saving space
BTW my Sierra drive is full, other wise I would just drag those files over...
Any thoughts..