There are two possibilities to change firmware on the Beacon kit:
1. With a connected programmer
The nRF51-DK serves as a programmer in this case, if you have any other compatible programmer, you can possibly connect that programmer to your Beacon kit with an adapter cable. If you do not have any programmer now but would like to use one, I would by the nRF51-DK kit and use it as a programmer.
2. Via the bootloader
To upload a new application to the beacon kit, take an applicaiton hex file you would like to upload and bundle it together with an init file into a .zip file. Then upload that zip file with e.g. your smartphone to the beacon kit and then power-reset your beacon kit. Then a new applicaiton should be running on your device. To do this, follow the instructions given in this blog post.
