Moving measure

For some reducing stretch is enough, see https://musescore.org/en/handbook/3/layout-and-formatting#increase-decr…
But not in all those cases. Why using these vertical frames all over the place rather than letting the score flow?

Indeed, those frames don't seem to make sense. I guess maybe they were added to create some extra space? Spacers are better used for that. But they aren't needed here, and in fact they are kind of counterproductive - they lead to uneven spacing, in cases where it isn't needed or appropriate.

Line 5 is bar 12. If you want 12 bars to take two systems, best would be to remove the break you have after bar 5, also the frame, then you would have 6 bars on each system. Really, though, once you remove the frames, you will find you have more than enough room to go with 4 bars per system, which fits more comfortable and is pretty common on tunes like this.

So, right-click on frame, Select / All Similar Elements, then hit Delete. Then Ctrl+A to select all, then Format / Add/Remove System Breaks, accept the default of every four measures, and hit OK.

You'll see everything fits on three pages with tons of room to spare. So then add page breaks so that instead of seven systems on the first page, then eight, then only four, you have 6, 6, 7 or 6, 7, 6.

Then go to Format / Style / Page and re-enable vertical justification so the systems are spread out across the full pages instead of bunched up at the top. Or at least increase the minimum system distance to achieve the same effect.