How do

Change default don't appearance?

Do you mean the font? There is no way to change the default font for everything you post. That must be changed in the vBulletin code by admin. You can change the font of your individual posts by using the GO ADVANCED button under the text box when making a reply post and selecting the font style and size from the tool bar above the text field. Same applies when posting a new thread but the advanced options are already there.

Dave,
For some reason my font size is always small compared to original post. Thinking perhaps all I needed was a default.