Change in Credit Control area

Currently we are using different credit control area for different sales area

Sales area Credit control area

1001-10-00 CCA1

1001-10-01 CCA2

1001-10-02 CCA3

now we would like to change credit control area and make it one for all the sales area, i.e.

Sales area Credit control area

1001-10-00 CCA4

1001-10-01 CCA4

1001-10-02 CCA4

if somebody worked on change in CCA please guide what all things has to be done for changing the same, especially for the value of Credit Exposure in old CCA (open items)

regards

Rajesh T.