This guide will tell you how to change the title & banner in Rocket League.
When you start the game, you will see your title and banner on the left side of the screen. 
You have to go to your profile, select “Choose Banner” and you can choose any from your collected banners.
Then to its right, you can choose a title that you have collected.
You can also choose a multi-colour banner. If the banner is multi-colour, then a paint bucket will appear on its right before the title.
You can also choose avatar borders for your collected avatars. There is a paint bucket next to the avatar button, you can use it to change the colour of the avatar.
Playing on PlayStation is a bit different. Any avatar on your PlayStation is the actual avatar of the game. If you visit the edit profile, you need to go to the avatar option and you can choose any avatar from the PlayStation menu.