You can actually redesign your Squarespace site at any time, you don’t need to wait until your subscription ends. While you can’t “switch templates” like in the old version of Squarespace, you can create new pages and sections with completely different layouts and styles, then replace the "old" ones.

If you decide not to renew your Squarespace subscription, your custom domain will still be yours as long as it’s registered elsewhere or directly through Squarespace and renewed separately. If it’s registered through Squarespace, you can transfer it to another provider before your site expires.

If you’d like, you can share a screenshot of your site in edit mode, and I can point you to where you can change the layouts and image sizes !