Login to Admin Mode and go to the page on which you want to make changes. Click on that page's link in the navigation.

Once you are on the correct page, locate the block that contains the content you want to delete. Hover your mouse over the "Block" box or link for that block and the Block Menu will appear.

Click the "Edit" link on the Logo Group Block Menu. You will then see your Logo Group block and it's content.

Hover over the logos in the "Active section" and you can change the display order or remove any of them from the Logo Group. You may do so by clicking on the button beside the logo: You can move it "UP" or "DOWN" or click on "X" to remove it.

Click on the [Save Changes] button once you are done editing.