How can I legally recover money from someone?

I had given a lump sump amount to a transported to help his business, accordingly we agreement on Rs500/_ stamp paper, where he is committed to pay the entire amount within 36 months equated monthly installment. But now a days he is not making the installment in time and fail to pay last month installment and request me to wait for some more days as he is not financially not good at present. I have 2 cheques issued by his name as well as his firm name with entire amount when the agreement was made. Now what should I do to recover the entire amount.