What Windchill api's needed to modify existing wtpart structure?

I have successfully created a wtpart structure in Windchill by using WTPartUsageLink.newWTPartUsageLink(). Now I want to modify that structure by either deleting an existing component or by changing the quantity of an existing component. Can someone point me in the correct direction as to what api(s) I need to use to accomplish this?

Existing structure:

wtPartAssembly

• wtPartComponent1
  • qty = 1
• wtpartComponent2
  • qty = 3

What api(s) needed to delete wtPartComponent1 and change wtPartComponent2 qty to 1?

Thanks Randy Jones