You can edit your profile page by clicking "Edit profile" after logging in.
You can also upload animated GIF images for your profile after registering as a pixiv premium member.
* Maximum allowed profile image size is 5MB/image.
* Supported image formats for upload are JPG, PNG and GIF.
* In the case of animated GIF, a maximum of 20 frames all formatted to the same display size is allowed.
* Animated GIFs wherein the display size changes between frames is not allowed.