It's great to hear that you're interested in becoming a full member!
Your friend, who is an existing member, would need to first remove you as their buddy. It's really easy, they just need to head to the 'Account' section of the app, enter the 'Your Gym Buddy' page and select 'Remove'. Within two days of the removal, you'll be able to start a new membership by logging into your Member's Area and selecting 'Restart Your Membership Here'. Alternatively, head to the 'You' section of the app and then to the 'Gym' page, where you'll see the option to 'Restart your Membership'.