Making a bigger cage for a leopard gecko?

so i just got a leopard gecko and i have it in a 10 gallon and i also have another 10 gallon fish tank but sadly all the fish died of old age so i remember that the glass is glued on by silicon and im thinking of melting the glue of one side of the fish tank you know the sides that are small and are to the left or right and then melting the other opposite side of the leopard geckos tank so then if can put them both side to side together and glue them on with a non toxic animal friendly glue can you please help me i dont know how to melt or take off the glue