Having a leaking window is a sure way to get a headache. It not only leads to damage related to structure and lots of mess, but also triggers formation 
of mold. Fixing a leaking window as early as possible is the most effective step you can take, and this step basically requires taking out the window and repairing the wood frame or the sash, and the trim surrounding it.
The following steps should help you repair your leaking window in a proper manner:
Step 1:
At first, the inside window stop which retains the bottom sash (wooden frame of window) in the right place has to be removed. For this, hammer by using a flat small pry bar, or a putty knife. If you can, remove the stop in a single piece.
Step 2:
Now have the window removed, and put it in a good work space. In case you find a rope attached to the top of the window, know that the window you have is double hung one. In such a situation, driving a big common nail inside the trim and then untying the rope from the body of the window should help. After this step, remember to tie the rope around the nail. When you do this on both the sides, removal of the window should be easy.
Step 3:
You should now take out old glazing pieces, laying the window nicely on work surface. The more pieces you take out, the better. Being careful to keep the glass from harm, perform this step on both the window sides with the help of a putty or utility knife.
Step 4:
If you can find window points which have come loose, replace the points. Using a tip of screwdriver, you can easily insert new window points. Make sure that you push the sharp edge of the point as much as possible into the wooden frame, and that the point rests on the glass surface, which is required to keep a window in the right place. Using a small-sized hammer, give a gentle tap on the screwdriver’s end to complete this task.
Step 5:
If there is bare wooden parts along the glass edge, cover the bare parts using latex primer paint. Continue your work only after the paint dries.
Step 6:
Opening a glazing compound can, press the same into proper place using putty or glazer’s knife. You can heat the knife tip using propane torch in case you need very smooth finish, for which only a little amount of heat is required.
Step 7:
The fresh glazing compound should be painted using sealer coat as well as trim paint. If you prefer, you can perform this step after placing the window in its right place.
Step 8:
In the same way you found the sash cords attached to the window sides, re-attach the cords after putting the window back in its proper place.
Step 9:
Having replaced the window stop, make it a point to paint the window using matching trim paint.
Keep in mind that with the use of the tip of utility knife, cutting the paint of a window trim which is painted into place is quite easy. Also, note that you should never ever try repairing glass with broken seal. In case a glass develops crack, replacing the glass after removing the window is your only reasonable option.
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