Not sure whether I am unable to find a major feature or It is actually not there … but …
How do you actually edit tags? Suppose you have a mispelling: how do you actually correct it?
How do you actually delete unnecessary tags?
I can’t actually seem to find this anywhere in the app. Maybe I am missing something …
Thanks for your help! 
I think there is currently no global tag editing function integrated at least I haven’t found any. My solution is to set a new tag for a note. An unused tag seems to be deleted automatically or at least it disappears in my tag cloud. You can enable or disable a tag by clicking/taping on it.
This solution will unfortunately be a little annoying if you’ve set a misspelled tag to many notes and not only few.