If you are an individual and want to declare yourself insolvent, you need to file for sequestration.
Sequestration should not be taken lightly - you will lose all your assets, sold to the highest bidder and it has serious implications to your credit record. You will not be able to borrow any money and you will be listed with the credit bureaus for a period of 10 years.
If you are applying for insolvency on behalf of a company or business, you will file for liquidation.