purge HH which didn't ...

[shahrad]

see a flop and/or which didn't go to showdown, without losing the stats.

[kraada]

There's no automated way to do that at this time.

Also by doing that the hands you have left would give you some very strange looking stats - I imagine VPIP and PFR would be skewed considerably - so I'm not certain whether it would be the best of ideas.

[shahrad]

HM1 does this without skewing the stats.

[WhiteRider]

Stats are based on the hands in the database, so it isn't possible to remove hands without affecting the stats.