A remission of debt granted to the principal debtor discharges the sureties, even joint and several.
A remission granted to one of the joint and several sureties does not discharge the principal debtor, but discharges the others to the extent of its share.
What the creditor has received from a surety for the discharge of his surety bond must be set off against the debt and discharge the principal debtor in proportion. The other guarantors remain liable only after deducting the share of the discharged guarantor or the value provided if it exceeds that share.