The easiest way to change your current Polkadot Tiger plan is from the Subscription section. 

If you are logged into the tool, you can see the settings icon in the top right corner of the screen. Navigate there and select the Subscription option from the menu.

Under your Current Plan you will see two buttons. Click on the Update plan one. This will take you to a page where you can change to another pricing plan.

Below the Plans Available title you can filter the plans either based on the Monthly (plans that are charged each month) or the Yearly options (plans charged annually).

Select the filter you are interested in and choose the plan you want to switch to by clicking on the Continue button next to its name.