P.S.: It would be a good idea to start with adding a profile pic, so people can see you are a real person, and not a bot. You can add your profile picture by going to your wallet. once you're there, you will see a link called 'Settings' in the menu bar on the right (next to 'Wallet').

There, you can add a profile pic and a header background.

If uploading won't work - which happens sometimes - you'll have to do it on Steempeak. It is the same site as SteemIt, but with a different layout.
Log in there with your private active key.

Then, when on your profile, click the 'Actions' button and select 'Edit profile'. You can then add your images in the popup window