You can change a contract after it is signed, but it is not enforceable if all parties do not agree to the changes. All parties should add new signatures and be given copies of the new contract. You may need to amend a contract if you need more time to complete a project, your supplier has postponed their delivery date and materials to you, a key team member leaves the company or many other reasons. How to modify a contract:
Make small changes by simply handwriting them and signing the change
Make a new contract and have it signed
Add an amendment and attach it to the original contract
Make a new contract using strikethroughs to show what sections were changed
If the original contracts include agreements about the contract not being amendable, you may not be able to change the contract.