I bought a tool awhile back which I have found to be very handy.
It looks like an oversize green hocky puck with a V cut across one face and various holes drilled in it.
You place the barrel in the V groove and then use a brass punch and a hammer to work on dovetails.
You could make one of these with a hockey puck, or you could simply use a roll of masking tape in a pinch.
I buy various diameters of brass rod stock from the hardware store to use as brass punches. That way when they get too banged up I just cut another length. Cost is next to nothing compared to replacing a punch.
Generally a dovetail has a slight taper in one direction or the other. If you examine it closely, you can often tell which way to drive the sight out. If not, you'll figure it out when the sight sticks and won't drive any further. That's your cue to turn it over and drive it out the other direction.
I believe 'out' is usually left to right.
If the sight needs fitting, file on the flat surface on the bottom of the dovetail on the sight. Do not file the dovetail on the gun. Do not file on the sides of the dovetail.