过and庆祝are not the same. I think 庆祝is closer to the meaning of celebrate, which means we do some activities together for a happy thing.
But 过means to pass or spend the special days as we are supposed to, no matter a happy day or sorrowful day.
So only for a happy days, 过 and 庆祝 can both be used. Like 过/庆祝生日，过/庆祝春节，过/庆祝圣诞节，过/庆祝结婚纪念日。
The following phrases are not interchangeable：
庆祝比赛胜利(victory of a match)，庆祝他的成功(his success)（过X）
过清明节(Tomb Sweeping Day)，过周年(one year after a person's death)（庆祝X）