Change the zoom level of your database diagram to control how much of the diagram you can see on your screen at once.
Zoom a database diagram
Note To edit tables, you must set the zoom level to 50% or higher. To create relationships, you must set the zoom level to 25% or higher.
Zoom to a selected object
Tip
To center the entire diagram in the window, use Select All to highlight all objects in the database diagram and then choose Zoom Selection from the Zoom submenu on the View menu. This will zoom your diagram to fit in the current diagram window size.