If you’re subscribed to a project, it’s very easy to upgrade to a different tier to access certain rewards. Doing so instantly allows access to the posts you want to see.
If you’re currently on the Donation tier, you won’t be able to access any locked posts until you upgrade.
Here’s how to do it!

A screenshot of an example project page. The project is called “I am the trash man!” and the cover image is of Danny Devito. On the left side of the screen is a supporter tier. The prompt “Change subscription” is surrounded by a red box.
Here you can see a user is logged in and subscribed to a $1 tier of this example project. The link to change your subscription is highlighted in red. Clicking the button takes you to the “Upgrade or change your subscription” page

This button is also available on individual post pages, highlighted in red.

After clicking “Change subscription,” you will be on the “Upgrade or change your subscription” page. In this example you can upgrade a subscription, pay the $11 difference, and access the locked content from the higher tier instantly.
You can also -
If you want to cancel a subscription, you can do so on the “Manage Subscriptions” page, and you will have access until the end of the month.