Currently our posts-per-page is set to 20 for people who haven't changed their defaults in their User CP, and for guests.

Starting immediately, I'm changing this to 10.

If you're a registered member, and want to continue at 20, or change it to some other number,

1) click on User CP at the top of the page
2) click on "Edit Options" on the left
3) about 2/3 of the way down the page, there's a setting for "number of posts to show per page"
4) Change this to one of the drop-down choices and save it