When circumstances change a court order needs to be varied rather than
unilaterally deciding to reduce the amount. Until the order is varied your
partner is liable for any arrears which may be enforced through the courts
like any other debt. When making an order though the court has to take in
consideration the ability of a debtor to pay and take into account a basic
level of subsistence.
Changing CM is usually relatively easy
if the order was made after March 2033 and has been in place for a year.
Your partner could apply to the CSA for assessment, the CSA notifies the
court and a
consent order in relation to CM ceases o have any
effect.
The exceptions to this would be when one parent lives
abroad, there are step children, over 18s in education or if the order
was worded in such a way that a global amount (CM+SM) should be paid minus
any payment made through the CSA.
However, your partner would
still need to apply to vary SM through the courts.