Sure, what you'll need to do is the following:
1. Delete all plans in Monto
2. Recreate the plans with the new pricing
3. Update pricing for the associated products in your Webflow ecommerce store settings
Please note it's best to do all of this fast because during the period where there are no plans in Monto and you get a purchase that customer won't be added to a subscription, so best to do it quickly and during a low traffic moment.