Edit text length before “read more button”

Hi Guys,

Pretty new to wp so hope this isn’t an (too) obvious question; I can’t seem to edit te text length before the “read more” button/code, it stops automatically at about 25 words. If you check the following link, you can see at the homepage some posts are cut off right in the middle. When i try to check the option box for “full article display” it doesn’t work as well, while the “summary” only displays about 25 words. Any tips or tricks for this one?

Thanks in advance!