To adjust the margin: Right-click in the chart area > click Configure > in the Margins settings on the right-hand side, change the value for “Price axis top bottom margin”.
This can now be done with the newer versions (5.4.0.0+) of DAS Trader Pro using Hotkeys. Please see how to do this in our forums: https://forums.bearbulltraders.com/topic/1239-chart-y-axis/?tab=comments#comment-8556