Make sure you are in Dimension
mode 
. (You can also do this while in Select
mode 
.)
Move the cursor to the dimension or the dimension line. The dimension changes from magenta to bright green.
You can modify a dimension by entering a new value in the Dimension dialog. The Dimension dialog appears when you first assign a dimension, or whenever you double-click on a dimension.
To modify a dimension using the Dimension dialog:
Make sure you are in Dimension
mode . (You can also do this while in Select
mode .)
Move the cursor to the dimension or the dimension line. The dimension changes from magenta to bright green.
Click on the dimension. (In Select mode, double-click.) The Dimension dialog appears, displaying the exact value of the dimension.
In the Dimension dialog, enter a new value for the dimension.
Click anywhere to define the dimension (or click exit or press Enter).
The entity is resized to reflect the new dimension.