Hi,
First thing you need to do is make sure the new springs you bought are for the same weight of sash as the old ones.
The springs come in weight ranges like 20 pounds to 30 pounds, 30lbs to 40lbs..etc.....you can adjust the tension on the springs by using a spring balance tool...this attaches to the bottom of the springs and you pull it out of the round casing and turn it either clockwise or anti clockwise...depending if you need more tension or less...so you get the correct amount of tension(weight) for your sashes to balance.
Fitting them is quite easy...there will be a screw at the top of the spring,which is fixed to your window.....before you remove this screw you need to lift the window up and with the spring balance tool,pull the spring down and twist it so its no longer attached to your sash(if you don't do this,there is a chance of something breaking and flying out under tension,which could be very dangerous...chance of something breaking and hitting you in the eye is small....but why risk it
....USE BALANCING TOOL TO REDUCE THE TENSION OF THE SPRINGS BEFORE UNDOING ANY SCREWS.
Close the window after doing the above and remove the screw at the top...you might be able to get the old spring out by just pulling it out...if you cant you will have to remove one of the staff beads(molded bead around the inside of your window)IF THE OLD SPRING WONT COME OUT EASILY THE NEW ONE WONT GO BACK WITHOUT YOU BENDING IT,AND THE NEW SPRING WONT WORK IF ITS BENT
If you have to remove the staff bead,remember to disengage both springs from the sash with the spring balance tool(which is shaped like the handle which you would raise and lower a car jack...with a hook on the end of it)
Once the sash is out. Attach one of the new springs to the frame(The side where you didn't remove the staff bead) and the other one in the groove of the sash and side the sash back into place.
Fix screw at top of both springs,slide sash up and connect springs to the sash via the metal plates under the sash.
Once both are connected ,its just a matter of balancing the new springs which means attaching balancing tool ,pulling spring out of round tube and turning a few times until your sash is balanced.
Don't forget to put staff bead back again
