To program for the first time, you can use a debugger, connected via the SWD/JTAG port, or use FlashMagic to program via the USART.
For the debugger, you will need a debug probe, such as LPC-Link2 or the new MCU-Link, which cost about $15 each and to use the free MCUXpresso. You will also need the SWD circuit described here
https://community.nxp.com/t5/LPCXpresso-IDE-FAQs/Design-Considerations-for-Debug/m-p/469565
If you are going to write any code, having a debugger will save you a lot of time, so it is better to make sure you can use it from the start, rather than have to re-engineer you board to add it later.