If the dimension was placed using the Insert > Model Items method, just double click the value and type the new value in the Modify box. Doing this will affect the model size.
If the dimension was placed manually using the Dimension tool, a single click will open the Dimension Manager, and the Primary Value > Override value option can be used.
Doing this will not affect the model size.
IMO this option should never be used to change a value. It is a bad practice hang-over from 2D drawing packages.
Okay I get the difference. I added a model view to the sheet and then dimensioned it. When I double click on the dimension I don't get a dialog box to change the dimension so the part will update.
You would serve yourself well to go through the SWX tutorials, especially the drawing section. What you have asked for is a simple capability of SWX. If you go through the tutorials you'll find many other capabilities that will dramatically reduce your workload.
While drawing dimensions can be used to drive the models feature sizes, it is not the best method. Changing the features via their underlying sketch dimensions is the safest method, and preferably while in an assy so that the consequences of the change can be seen in relation to the mating parts.
