To sign a sponsor agreement simply click the button with the 'shaking hands'. The agreement is signed for the complete duration shown in the offer; if you want to replace an agreement prematurely, you'll have to pay a termination fee.
You can sign a follow-up sponsor agreement while your current agreement is still active. The follow-up agreement becomes active as soon as the current agreement expires.
To replace your current agreement with the follow-up agreement, simply click on the 'down arrow', but make sure you pay attention to the early termination fee.
The follow-up agreement can be replaced for free at any time.