I think they're unsealed hubs. In which case, take it off the bike, loosen the nuts on the ends on each side, then tighten the ones after them by hand.
They don't need to be silly-tight, just tight enough so the axle can move without any play.
Once you've done that, get a thin spanner (Argos bikes etc come with a shitty tool kit, which has ones the right size ) and hold the cone whilst you tighten the nut up to it to lock it in place.
You might find yourself doing this quite often, I did and had no idea how they were coming loose when the wheel was always tight in the frame!
I bought a sealed hub in the end.