You should open your profile, place the mouse cursor on your Hourly Rate digits and you will see a pencil icon. Touching to this pencil open "Change Hourly Rate" window. Now you can change it.
Best regards, Vladimir
You're an exclusive member of your Agency and can edit your profile rate from your Agency account, by going to Find Work > Agency Roster > checking the box in front of your name > selecting Profile Rate from the drop-down menu under Change Roster Settings > clicking Apply and Update Rate once you're done.
Alternatively, you can change your status to non-exclusive by going to your Agency account > Settings > Members and Permissions and editing your status under the Agency Freelancer column. This will allow you to change your profile rate directly from your Freelancer profile.