Changing "Primary" Edition?

[Paul]

Usually when I combine books, what I'd consider the "right" edition (the one with the most reviews, with a cover, with good edition details) becomes the "primary" edition, but other times, it doesn't quite work out that way.

For example, when I combined this book with the arabic version (as is recommended by the "Do combine" stats), the Arabic version became the main version!

And this version has an edition that has a cover, and that one should probably be the main edition, but I don't know how to make that so. Anyone know how to change the priority ordering on these things?

[Scott]

The most popular (most-shelved) edition is the primary by default, but authors can change it if they have an author account.