I am not able to update apps in my Windows phone. When I go to store it is showing error. I am not able to back up also. If I reset my phone I will lose my contacts & messages. Help me please.
If you have an older Windows Phone 8 device, it is no longer supported. As I recall this means that the Windows Phone 8 app store is also no longer available. Windows Phone 8.1 also ended support in July 2017. Please see https://support.microsoft.com/en-us/help/4036480/windows-phone-8-1-end-of-support-faq
Contacts should be in the cloud somewhere depending how you set your Live account and whether you linked it to outlook.com or not. Email should be in the cloud as well on which ever email account you linked to your device e.g. Gmail, outlook.com etc.