How to remove the top sash of a medium size new double glazed window

You would not need to have a jack to be able to lift something up. Through the use of some pieces of framing material (such as common 2x4's as they are called here in the USA) you can pry and lift things with relative ease by the mechanical advantage of a lever. Cut the vertical piece to just the right length for the application and then with the help of at least one of those four friends you may be able to get the upper window into place.

Some things to think about with this.

1) The window may actually be stuck in its frame and unable to move. The wood over the years could have swelled and locked the window in place.

2) Coats of paint applied to the window and the frame may have locked in the window as well and thus not be movable at all -- unless the paint was all removed first.

3) If you do try the lever bar approach shown in my picture make sure to apply the pressure to the window near the frame under the side rail of the window. To apply in the middle away from the rails will put undue pressure on the glass and could result in breakage and / or personal injury.

4) Applying excessive pressure in one spot, either on the window itself or on the sill area below can damage the wood. This would be especially true for windows that are made of softer type woods like pine.

5) When using a lever scheme take the time to plan out the activity and how it will be setup. Without careful setup and applying pressure to the lever in the correct direction you could cause the fulcrum board to kick out sideways and pose a danger to either yourself, the window glass, something outside or someone below the window area.

These windows must have been installed into window casements that were built in place or reused from previous windows. The reason I comment about that is that if the windows were new units with the windows themselves pre-hung in the casements it is hard to believe that they would have the misfit that you describe as delivered from the factory.

In any case you would do well to see if you can talk one or two other contractors to come out to look at the installation to see what feedback they would give to you.

Sounds to me like you need to argue the case for a replacement set of new windows. If by chance you have not paid for the job you should withhold such payment until the problem is corrected to your satisfaction. If you have already paid then you have lost a certain amount of leverage but threat of a civil suit may be in order if you do not get a suitable response from the contractor. Of course you have to weigh the cost of getting involved in litigation against the size of investment already made in the windows.