Hank here from Shopify!
Normally, you can change your plans within your admin by going to Settings > Plan and permissions, however, annual plans work slightly different.
Depending on how long is left on your plan, or if you have the likes of carrier calculate shipping (CCS) installed may mean losing certain features but these can be individually reviewed by our billing team which I can certainly assist with.
If you want me to follow this up with you, let me know and I will send you an email to verify your store!
Alternatively, if you want to get in touch with our live support, you can contact them here.
All the best,