This isn’t really a straight forward task. From what I know in 1.7 there is a command but that is development only. So I’m running 1.6 and to see the config for my replica set I run

rs.conf();

I get the following output

> rs.conf();
{
        "_id" : "core",
        "version" : 3,
        "members" : [
                {
                        "_id" : 0,
                        "host" : "mongo1.domain.com:27017"
                },
                {
                        "_id" : 1,
                        "host" : "mongo2.domain.com"
                },
                {
                        "_id" : 2,
                        "host" : "mgmt1.domain.com",
                        "arbiterOnly" : true
                }
        ]
}

Now I have two members to my replica set plus my arbiter. So I want to remove that so I can add another one. So I run the following

> use admin;
> cfg = rs.conf();
> cfg.members.splice(2,1);
> cfg['version'] = 4 
> db.runCommand({replSetReconfig: cfg});

Then it will be removed. You can see my version was at 3 so I upped it to 4 so mongo will know there was a change. Now if I check the config I get the following

> rs.conf()                                                                                                                                                                  
{
        "_id" : "core",
        "version" : 4,
        "members" : [
                {
                        "_id" : 0,
                        "host" : "mongo1.domain.com:27017"
                },
                {
                        "_id" : 1,
                        "host" : "mongo2.domain.com"
                }
        ]
}

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