Thanks for reaching out! The 280-character limit for Twitter posts includes URLs, so if you are including a link, your effective character limit is 257. The character count within the social publishing tool will automatically adjust for the shortened link once a URL is added, but the link itself will not appear shortened until your post is scheduled or published. Images also count as links for this purpose, so including an image in your post will also use 23 characters.
Regarding the image, you can remove it by clicking the insert image button on the bottom of the left hand side, pick a different image and then once it pulls in the new image you should be able to see an option to remove the image once you hover over it.
