Alexandra,
For example I have an interface such as:
!
interface vlan.0.202
ip address 10.202.1.1 255.255.255.0 primary management
no shutdown
exit
I will change it to 10.202.1.2 as follows
enter configuration mode :
S3 Chassis(su)->configure
S3 Chassis(su-config)->int vlan.0.202
S3 Chassis(su-config-intf-vlan.0.202)->shutdown
S3 Chassis(su-config-intf-vlan.0.202)->no ip address 10.202.1.1 255.255.255.0
S3 Chassis(su-config-intf-vlan.0.202)->ip address 10.202.1.2 255.255.255.0
S3 Chassis(su-config-intf-vlan.0.202)->no shutdown
S3 Chassis(su-config-intf-vlan.0.202)->
Of course you want to make sure that you are not using the interface that you are changing.