How can I change cover image and avatar ?
You need to have a DTube account and log in with it, then you need to go to My Channel and go in to ABOUT section, finally click the red EDIT button.
You can edit your information from this section and image and cover url should be in the same format like the picture above. Make sure you link to an image (.png, .jpg, etc), and not to a webpage.
For the cover image you can use something between 1900 (width) x 265 (height) or 1354 x 155 to check for best results.
For the avatar, a square picture (same width/height) is recommended. The maximum size your avatar will display on the site is 128 x 128