Yes, you can upgrade Pepwave devices from 6.3 to 7.1.0 without any problems as long as the models are supported by this firmware version.
Please read the following forum post for more information:
Please note that the following models will NOT be supported by Firmware 7 onwards. Rather, they will
receive Firmware 6.x maintenance releases as needed:
MAX BR1 HW1
MAX BR1 Pro HW1
MAX On-The-Go HW 1
Surf SOHO HW1
BR1 and BR2 IP55 HW 1
Balance 305 HW1
Balance 380 HW3-5
Balance 580 HW1
Balance 710 HW 1-2
Balance 1350 HW1
Please note that the following models are not compatible with Firmware 6.3.0 onwards: