nimalsiri48 Hi there,
All giffgaff SIMs are 3 in 1 so if the SIM is less than four years old then it should just pop out into a smaller size as shown in the video below…
If the SIM is too old to change size (quite likely as you have been a member since 2013) then a SIM swap is necessary. All this means is that you need to order a new SIM here: https://www.giffgaff.com/orders/mgm and then activate it when it arrives here: https://www.giffgaff.com/activate
Make sure that you activate the new SIM from your original account, you will know that you have done this correctly because you will get an option asking if you would like to keep your original number.
Find out more about SIM swaps via this useful video:
The SIM will take a few days to arrive once ordered and then the SIM can take up to 24 hours to activate.