If you have forgotten your login you can click on the following link https://hal.archives-ouvertes.fr/user/lostlogin (your email adress will be required).
If you have forgotten your password you can click on the following link https://hal.archives-ouvertes.fr/user/lostpassword to ask for a new one (your login will be required)
You will be able to change it afterwards directly in My Space / My Profile / Modify password