There may be a more correct way using the quickedit configuration screen in the Manager, but you try changing this code in the file assets/modules/quick_edit/javascript/quickedit.js
this.windowSettings = 'width=400,height=300,toolbar=0,menubar=0,status=0,resizable=1,alwaysRaised=1,dependent=1';
Note that your changes may be overwritten when you update MODx.