To change the pins in your schematic, click on U113 so it is highlighted then right-click it and select "Edit Part". Double-Click each of the VSS pins (not the labels) and it will bring up the Pin Properties window. Change the name to GND, Shape to "Zero Length", type to "Power", and un-check Pin Visible. Once you are done, close the window. Ignore any warnings about a pin with the same name. Then either update the current part or Update all if you are using the same part in multiple spots in your design.
If this works they way you want it to, you may want to consider changing the library part so you will not need to modify the individual parts the next time you use it.