Dear Sir

           I have a subscription of office 365 and i had already install one Computer and it working correctly. But Now i want to change  its password from that one Computer . But i am unable to login in my account.

Hi,

By "i am unable to login in my account", would you please be more specific?

Since the question is related to your Office 365 subscription and account password, probably you need to post the question in Office 365 Community forum, detail your scenario a bit, the experts will provide you the appropriate suggestion for you:

http://community.office365.com/en-us/f/default.aspx

If you have any questions and feedbacks about Office client products, feel free to post in our forum. :)

Regards,

Melon Chen
TechNet Community Support