What to do when the storage limit is exceeded in salesforce?

As you might have known, Salesforce works on multi-tenant architecture which puts some governor limits across the system. Data storage is one of them. it depends on per User Licence in different Salesforce editions.

Please find the table below with different editions. Regarding storage limits exceeded in salesforce - Storage is divided into two categories: file storage and data storage. File storage includes files in attachments, the Documents tab, the Files tab, the File field, Salesforce CRM Content, Chatter (including user photos), and Site.com assets. Data storage includes the following:

Accounts Article types (format: “[Article Type Name]”)

Article type translations (format: “[Article Type Name] Version”)

Campaigns

Campaign Members

Cases

Case Teams

Contacts

Contracts

Custom objects

Email messages Events

Forecast items

Google docs

Ideas

Leads

Notes

Opportunities

Opportunity Splits

Orders

Quotes

Quote Template Rich Text Data Solutions Tags: Unique tags Tasks

Go to Setup-> Data management-> Storage Usages and check which object is using the most space.. If you think that any object which is not useful to you and has most of the space you can delete those records but if you need you can purchase extra data space from Salesforce.