Inside a project, access Project Settings by clicking on the bold project name in the upper left, and clicking "Project Settings".
Inside project settings, you can:
View/edit project information (e.g., client, due date)*
View/edit project collaborators or invite new collaborators**
If you are the owner, you can transfer ownership to another project collaborator
Leave a project (you may need to transfer ownership prior to leaving)
*Only project owners can edit project information
**Only project owners can remove project collaborators; all project collaborators can invite new collaborators.