Yes !! you can, if you have given us the Power of Attorney to us for your depository account and the stock that you are selling is in your depository account with us. To get the sale value you need to sell the stock using product code CNC (cash N carry). However, the sale proceeds will not be available for making a fresh purchase immediately due to time gap in settlement of funds. When you sell a stock from your demat account, the funds will be released on T+2nd working day from the exchange and hence, there will be no free cash available on the same day when you sell the stock from CNC.
There is also another rule that if you buy stocks / futures / options you need to have the minimum peak margin requirement before you place the orders. Read here to know about peak margin. In this case, as you sold the stocks on T day, you will not have the sale proceeds as free cash on T day itself. Hence, you will not be able to use the sale proceeds to buy an option / futures / equity cash on the same day but can use them on the next day.
For example if you sell stocks worth Rs. 1 Lakh under CNC then you will get CNC for Rs. 1,00,000 on T+1 day. With Rs. 1,00,000 you can trade in Equity Cash / futures / Equity options / currency based on product codes and their applicable margins on T+1 day.