on fifth of february i bought 50 shares of ULTRATECH at 6280. the stock increased and i sold all the shares at 6310 but the stock price went upto 6400. if i want to sell 20 at say 6310 and keep the remaining 30 for increasing profit which type of orders should be executed?

I think what you are looking for is the GTT / GTC orders. (Good till Triggered or Good till Cancelled orders). 

You can place a GTT / GTC CNC order for 20 units of ULTRATECH shares at your Limit asking price of 6310. These orders stay live in the server, even across many days until they are filled at your asking price or till you cancel them manually.

Check this thread for more info on when this order type becomes available on Fyers

https://community.fyers.in/post/gtt-order-601942c3bbc1dec471dba34a42

Meanwhile, you can set a price alert for Ultratech at 6310 on the Fyers app, on receiving the alert you manually place a CNC limit sell order for 20 QTY at 6310.