To change your membership type please login at - https://www.bsg.org.uk/my-account/
Click on the "My Subscription" on the left hand side. You should see something similar to the screenshot below:
When viewing your active membership, you should see a button to change your Membership Type (in red circle above).
Depending on your membership category you will be presented with a list of options similar to the screenshot below:
At this point make your selection of the appropriate new Membership Type by selecting the checkbox.
Then click on the 'Purchase' button then go through the check-out procedure to complete the purchase.
If you are switching to a reduced fee category in the middle of your payment year you will not receive a refund, however the system will extend your next renewal payment pro rata to a date further in time.