Need help in installing Norton - says I don't have administrative previlages

After entering the product key and downloading, my antivirus can't open. It keeps telling me that the download manager requires administrative privileges to download and install the product. What do I do? How do I get administrative privilege?

[Edit: Clarified subject]

Hi KingsleyNwokwu,

Could you provide your device type, such as, PC. Laptop, Mobile, tablet, etc.  What OS you're using, which Norton Product you're trying to install?