How to extend my legal stay in Costa Rica?
Countries that do not require a visa to visit Costa Rica can enter Costa Rica and stay there for up to 90 days. These 90 days cannot be extended and the tourist must leave the country after the expiry of the visa. They can re-enter at any time to apply for an additional 90 days at the discretion of the immigration officer at the point of entry.
In order to live in Costa Rica, you need to obtain a residence permit or leave the country every 90 days in order to extend your stay in the country (however, this is only possible for countries that do not need to obtain a visa to travel to Costa Rica).