If you want to change the e-mail adress or password with which you log into your Blog2Social account, please go to http://service.blog2social.com/en/login/ and log in as usual.
Click on the tab "Account" and you will have the option to change, both your e-mail adress and your password. After you have changed something, don't forget to save the changes!
If you like to change the email address you used to activate your Blog2Social license under "Blog2Social -> Premium", you can take a look into the following guide where is explained how you can do this:
How do I change the email address for an activated license?