Selling real property before satisfying the lien obligation??

I am considering purchasing a small stick-built home on 1.25 acres. I will finance 96.5% of the purchase via an FHA loan. In 5 years, I would like to sell that house, moving it off the property, and build a larger custom home on the same property. Since the original home and the lot wil be financed together, and therefore subject to the same bank lien, how would I sell the small home to be moved without paying off the entire original loan? Any insight is appreciated.