If the stickers are on your screen then simply peel them off and on the residue left behind apply spirit, nailpolish remover, perfume with the help of tissue paper. If the sticker is on the body of the car, stand the car in the sun for 1-2 hours to make the body hot, apply turpentine oil (matti ka tail) and dont rub it hard for some minutes, the sticker will soften up and u can easily take it off. If the sticker is on the body I would say leave it there and dont remove it because your car is 25 years old and if you remove the sticker there will be a difference of colour under the sticker and patches will be visible.