hello if you have spare sim just do sim swap
All newgiffgaff SIMs are 'trio' SIMs (Mini/Micro/Nano in one just push out the bit that you need to fit your phone) and are 4G/3G/2G compatable.
you will need to perform a simple SIMswap.https://community.giffgaff.com/t5/Using-giffgaff/What-is-SIM-Swap/ta-p/7320084
SIMswap does not work between 21:30 and 04:30 each day.
Your current number and any goodybag / credit will transfer as part of the process.
Don't forget to back up any contacts on your SIM as these do not transfer as part of the process.