I want to change my password.
パスワードを変えたいです。
パスワードの変え方がわからずに助けを求める場合は、以下のような表現も使えると思います。
Could you help me change my password?
パスワードを変えるのを手伝ってくれませんか?
How do I change my password?
パスワードってどうやって変えるんですか?
I don't know how to change my password.
パスワードの変え方がわかりません。
Could you please show me how to change my password?
Can you help me change my password? Asks someone to help or show you how to change it.
Could you please show me how to change my password? is a polite way of asking someone to show you how to change it.
"Can you help me change my password?
パスワードの変え方を手伝う又は、やり方を教えてもらうように頼む表現です。.
Could you please show me how to change my password?
パスワードの変え方を教えてもらうように丁寧に頼む表現です。."
There are two ways of saying it. The first one is a more polite and formal way of asking for help, whereas, the second one is a casual format which you can ask your friend.