Changing durations and consolidating rests

I am (very) slowly learning musescore and have bumped into a problem that I haven't found an answer for.

Let's say I have two measures in 4/4 time, both of which have four quarter notes in them. Now I decide that I want them as eighth notes with no rests between them; so the quarter notes need to be converted to eighths with them all in one measure. An alternative version of the problem is just converting note durations and have rests scattered rather randomly through the measure and needing to consolidate them where I actually wanted the rest.

I have, by trial and error, accomplished this in a (large-ish) variety of ways, but it always winds up being a long and clunky process. The general problem is that I wind up with things like eighth note, eighth rest, eighth note, eighth rest, etc., and then having to do a lot of cleanup to get things in the right order and with the rests consolidated/removed.

I know that I shouldn't delete the rests ( https://musescore.org/en/node/122606 ) but the way I am doing things I keep winding up with a bunch of rests between notes and then doing a lot of clean-up. I have also managed to create measures with an "illegal" number of notes (too few) and then not been able to figure out how to add the missing note/rest.

Can someone please point me at an explanation or maybe tutorial of how this sort of thing is supposed to be done?

Edited to add a question about why this might be posting with my email, rather than my Username?