Do I have to withdraw my profits?

Any profit that you make from your trade(s) stays in your Upstox trading account.
Now, the next time you wish to trade, you can simply top-up that balance with Smart Transfer. Smart, isn’t it?

You have allocated ₹4,00,000 for trading and have made a profit of 50,000 from your trades on the same day. This 50,000 stays in your trading account; so you can re-use it for trading, the next day. However, if you choose to use the fund, you will have to withdraw it, manually.