Add a logo to customize your community, and contribute to the communities identity. The logo appears on the left side of the navigation menu, and when users click on the logo they are taken to your community's home page.
Tip: For the best results, the image should be a minimum of 300px wide or 60px high. Larger images are scaled to fit
Go to Admin Setup > Design > Banners and branding.
In the Logo area, click Change.
Click Upload Logo.
Use the file picker to select the image and optionally upload a new one to your library,
If the file is not already in your library
Click Choose file and select a file from your computer.
Click Upload file to add the file to your library.
Select the image from your library.
Click Save choice.
To hide a logo, choose the "Nothing" image, and to use the Medallia Ideas logo, choose "Default.