To help you organize or find your projects, you can enter file properties for them, such as a descriptive title, a subject, a project manager, or a comment .
When you first save your project, you set the project name or the project title. After that, you can change it at any time.
Click File > Project Information
Click Project Information > Advanced Properties.
On the Summary tab, type the new name in the Title box.
To get back to your project view, click the back button
Specifies general information about a project, including its file type, file location, and file size, company information, statistics, start and finish dates, and other properties.
The Properties command displays a tabbed dialog box. Select the appropriate tab for the type of information you want to view or type in case of the planner products.
General Tab 
Specifies the project name and other file attributes, such as file type, file size, and file location, MS-DOS name for the file, the dates and times when the file was created, most recently modified, and accessed.
Specifies the project title, subject, author, company name, manager, category, keywords, and comments.
 This is possible in case of planner products such as: Project Plan 365 for Win PC/Server, Project Plan 365 for Win Web/Server, Project Plan 365 Online Subscription, Project Plan 365 for SharePoint Server and Project Plan 365 for SharePoint Online