How can I change the background?
There is no such option on our site because we believe in the importance of a unified style.
If the background of the site has suddenly changed it's time to worry about the security of your account and perform a fast check with the vk.com/av scanner.
After this try to remember if you downloaded any third-party plugins or programs that promised "additional" features for VK. If so, please, delete them immediately for they can harm your computer and endanger the safety of your VK page.
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Try using other keywords, e.g.: "delete profile", "create chat".
Check your request for misprints.