To change something to another layer/sheet etc, there is a button (usually on the left) called CHANGE PROPERTIES. Click that button then select the ting you wish to change properties on. I.E. You made a nice lake, but you gave it the wrong FILL STYLE, put it on the MOUNTAINS sheet and on the VEGETATION layer. To change it, select CHANGE PROPERTIES, the click on the lake (to select it, click OK, and then from the menu, you can change the sheet, the layer and the fill style (as well as other properties)