i have server which running Centos and i want to change outgoing ip address.
following is my route and route list

[root@marketport tmp]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
184.105.17.96 0.0.0.0 255.255.255.224 U 0 0 0 venet0
162.245.223.0 0.0.0.0 255.255.255.0 U 0 0 0 venet0
169.254.0.0 0.0.0.0 255.255.0.0 U 1002 0 0 venet0
0.0.0.0 0.0.0.0 0.0.0.0 U 0 0 0 venet0

[root@marketport tmp]# ip route list
184.105.17.96/27 dev venet0 proto kernel scope link src 184.105.17.106
162.245.223.0/24 dev venet0 proto kernel scope link src 162.245.223.65
169.254.0.0/16 dev venet0 scope link metric 1002
default dev venet0 scope link

[root@marketport tmp]# ip route add default via 162.245.223.0 dev venet0 src 162.245.223.67
RTNETLINK answers: Invalid argument

[root@marketport tmp]# ip route add default via 162.245.223.67
RTNETLINK answers: File exists

anyone please correct me? where is wrong?
thanks you !

Try this way..
#route add -net default gw xx.xx.xx.xx dev ethX

As far as I can see, you already have a default route. That is why you are getting that error. Your default route is the following:

default dev venet0 scope link

You must change it instead of adding a new one. Try this:

[root@marketport tmp]# ip route change default via <gateway ip> dev venet0 src <your ip>

As lsalab said, you already have a default. There can only be one default, if there was more than one then what would "default" even mean? You need to change your current one, not add a new one.