If you are the owner of the account on the Personal, Team, or Enterprise plan, you can downgrade it whenever you need.
However, keep in mind some changes, which will happen with features after canceling a current price plan.

Downgrading to the Team plan

Note: When you downgrade to the Team plan, features, available on the Enterprise plan, get the limits and changes.

Downgrading to the Personal Plan

Note: When you downgrade to the Personal plan, features, available on the Enterprise or Team plan, get the limits and changes.

Downgrading to the Free Plan

Note: When you downgrade to the Free plan, features, available on the Enterprise, Team or Personal plan, get the limits and changes.