If you would like to place your custom installer banner, use Customize->Banner->Load Custom Banner button to Load Custom Banner.
MetaSetup has embedded banners, you cannot edit and Custom Banners but you can edit your custom banner and load it into MetaSetup
Required BannerSize is 160 x 380 pixel and can be imported from common picture formats such as BMP, JPG, PNG. You could upload different sizes of banners but they might break the layout of installer.
Update: it is definetely fine to have a banner size 160 x 380+ because the height will be cut automatically but not the width. We recommend you keep width 160 but make height aronud 390 because depending on choosen template the available height might be sligly different.