IF you already have a social security number, you don't need to change. If you only have a tax number, you can have it chaged.
工作單位原先用EAD, 要通知他們換綠卡嗎? 是否帶綠卡去就行? Yes.
還有其他要辦的事嗎? 回國是否隻須帶護照和綠卡就行了? Yes. 去別的國家如加拿大, 日本(原因是有大學踢球哥們還在那混)旅遊, 需要辦加拿大或日本的簽證嗎? I don't know.
先謝了!