Can my iPhone 7plus be updated

An iPhone 7 can be updated to iOS 15.7.1 at this time. That is the most current version it supports.

You cannot add local storage capacity to an iPhone. If you are running low on space you would need to delete content off of the iPhone, or move it to a computer or external storage device.

You don't need a link. You can check for updates any time by using your phone.

Settings > General > Software Update

If an update is available, you will know

As Mentioned , go to Settings ➡️ General ➡️ Software Update on your iPhone.

You can check what version of iOS your iPhone is running at Settings ➡️ General ➡️ About ➡️ Version