When working in a layout tab viewport it is sometimes easier to go back to the Model space tab and work on objects there, rather than activate modelspace mode in the smaller viewport in the layout.  I'll offer up a few ways to get to the modelspace area of a viewport when in a layout tab;

• Simply double-click on the viewport border.  This will flash you back to the model tab and add a red border around it.  Make your changes and then double-click on the red border or pick the square button, with an arrow pointing down and to the left.  This button is to the right of the Model/Paper button at the bottom of the application window.
• Pick the square button to the right of the Model/Paper button at the bottom of the application window that has an arrow pointing up and to the left
• left-click on the viewport to highlight and then right-click to get the pop-up menu. Choose Maximize viewport from the lower section of the pop-up.