You can change your collaboration offers and pricing under the Pricing tab in your profile.
To visit your profile, click on your tab at the top right-hand corner of the page, and select View profile from the dropdown.
To edit your collaboration offers and pricing, click on Settings in the sidebar menu.
Under Account settings, click on Pricing. You'll find all your collaboration offers and price ranges listed.
To remove an offer, click Remove. To edit one, click Edit under the collaboration offer you want to change.
Make any changes, then hit Save.
To add additional collaboration offers, check out this article.