Ray,
Just to make sure... If you are referring to this skimmer (http://www.coralvue.com/reef-octopus-nwb150-classic-protein-skimmer) that comes with an OTP pump, then yes, you can upgrade.
Here is the pump you will need...
http://www.coralvue.com/reef-octopus-bubble-blaster-2000-skimmer-pump
You will need to purchase the NWB150 adapter (on the same pump product page)
HTH,
Carlos
CoralVue