The update gives you greater control over the appearance of your profile page. For addicts like me, it's an opportunity to more extensively obsess.
You can now edit a board cover by hovering over it with your mouse. An "Edit Board Cover" button will appear (see below, left); click on it and you'll be able to rotate through all of your pins to select a cover image.
It's also possible to adjust the position of the thumbnail for a better fit, although you can't crop or resize it. Click "Set Cover" to finish. And you can choose board covers within each board by mousing over your pins.
Click on "Edit Board Cover" (left) to change the image.
Board covers were introduced as part of a big redesign Pinterest rolled out last month. Between then and now, users had no control over their board covers: by default, the latest pin served as the board cover.
Personally, I'd often find myself seeking out new images to pin if my board covers didn't look right. That's probably not normal behavior, but I'm sure I'm not the only one who did it. Did you? Let us know in the comments.