Nrf51822 more distance output power


I am using nrf51822 and i want to get more connecting distance between my phone App and my pcb device, i tryed to use set tx power to 4 but i do get any diference.
Do you have any example of code or how to set, i am using mbed compiler. I need better reconection of App if pcb device goes out the range.

Best Regards./Z odličnim pozdravom.