Yes, you may create as many copies that you want and give them away or sell them, while you do it in accordance with the GPL2 or later license and the conditions stated there. Whoever you sell it to is then granted the same rights as you have. You do not need to share your profit with us, ask us or tell us that you are doing it. It is all totally up to you. If you do sell the game though we would still appreciate a the info from you though even if you are not legally obliged to contact us, and if you like the game and want it to continue it’s development small donations from the sales would help the game a lot.