At the upper left, under the CF logo, click on User Control Panel. That'll take you to your Front Page, under the Overview tab, showing your current board stats. Click on the Profile tab, under the bold User Control Panel title. That will open your Profile menu. To the left, you will see the Edit Avatar selection, click on it, which allows you to upload an avatar image from your computer or link to an avatar picture located off-site.
I hope this helped you out. Looking forward to seeing pictures of your kitty or kitties.
Note the Maximum avatar dimensions; width: 120 pixels, height: 120 pixels, file size: 10.00 KiB.