Unless you know the exact IVs of the Pokémon, you probably won't be able to accurately find out. However,
you can erase your EVs with certain berries and start over. Anyway, your question doesn't belong here; this is forum is for team help and questions about it, and not game mechanics. You can ask in one of the Pokémon gaming forums instead (BW's
Quick Questions thread if the game is Black and/or White, for example).