Due to storage restrictions, your plan determines the number of active styleguides you can create.
Free plan: 1 styleguide
Basic plan: 1 styleguide
Team plan: 12 styleguides
Advanced, Organization, and Enterprise plans: Unlimited styleguides
☝️ Those on the deprecated Starter plan or Growing Business plan can be the owner of up to 12 active styleguides.
If you need more styleguides to work with, you can upgrade your plan by clicking the "Change Plan" button on the Billing page: https://app.zeplin.io/profile/billing