Help with script

Hallo, i started using unity 2 weeks ago and i’m not exactly an expert lol…
I create a javascript that spawn every 5 seconds a primitive object (sphere) and i just want to change the primitive with a imported model, someone can help me?
this is the code!
[15045-schermata+2013-09-03+a+07.21.48.png|15045]

One way could be to save your imported model as a new prefab and Instantiate it like this: