Thank you for contacting us. I can help you with changing your account, but I'm not sure why you would ever need to do that. Can you provide some information on what's going wrong? If I can understand the situation, I should be able to offer you better help.
Thank you for the extra information and your purchase! I think I understand what you need now. There is no options for signing out of an mSecure account. However, you can simply delete the PC and/or Android app from your device(s), and download it again from the Microsoft Store or Google Play, then sign in to your new account.
Were you able to get all your devices signed in to your account?
No problem at all Kostiantyn! Let me know if you need further assistance with this and I'll be happy to help.