This is specifically what I need to do:
I have mostly four-line text blocks separated by space throughout thousands of pages like this:

1
2
3
4

1
2
3
4

1
2
3
4

...and I need to make every text block look like this:

1234

1234

1234

I basically need to move the bottom three lines onto the first line in every text block, and I don't care if the space is removed afterwards, so that it looks like this:

1234
1234
1234

...How can I do this?