I own small restaurant d like to sell with one third down payment and the rest is with payments in three years. If they stop paying me how can I take

There are a variety of structures you can use for such a sale. Under the more customary formulation, you would create and perfect a "security interest" (i.e., a lien or mortgage) in what you are selling and retain the right to foreclose in the event of a payment default. Under an alternate formulation, you could place title in escrow and the buyer would obtain no ownership unless and until all payments were made. You need an attorney to assist you in doing this. It is not something you can do on your own. Feel free to contact our office if you need assistance.