You have to be on the 'Contract tab' to renegotiate contracts. You might need more rooms or the contract might be wrong, but you still have the option to make changes, if you tick 'Suggest Contract Update'.
You should then include a message for your supplier and specify the changes that you want.
Insert your message then click 'Submit'. The supplier will send an update of the contract. In this stage you are still able to suggest new contract updates. If you do not have any more changes, click 'Accept and counter sign'. Type in your electronic signature and click 'Submit'.