You can reset all counters, except those that are never reset, to 0 (zero) by issuing the admin stats, reset command:
admin stats, reset
If sampling has not been enabled using the stats_sampling parameter, counter values are zero. Running admin stats with a nonzero sample period sets the counters to zero, turns on sampling, turns off counter sampling after the sampling run is completed, and resets the counters to zero. If the sampling period is zero, current counter values are reported.
If sampling has been enabled, use admin stats with care. With sampling enabled using the stats_sampling configuration, counter values are accumulating. Issuing admin stats and specifying a sample period causes Replication Server to clear all counters and disable sampling (stats_sampling off) after the sampling run.