You can use DSCC to perform this task. For information, see Directory Service Control Center Interface and the DSCC online help.
Obtain an updated certificate from your CA.
Install the certificate on your instance of Directory Proxy Server.
$ dpadm renew-cert instance-path cert-alias cert-file
where cert-alias is the name of the new certificate and cert-file is the name of the file containing the certificate. For a description of all command options, see the dpadm(1M) man page.