You can upgrade or downgrade anytime in the settings on your profile. The desktop version makes this a breeze.
Step 1. Go to your settings. You will find settings under the cog icon near the bottom left corner of the page.
Step 2. There is a menu across the top of the screen. Select subscriptions from this menu.
Step 3. Choose your plan and provide your E-mail as well as card information. Follow the steps this process walks you through.