Is it the white dialog box that tells you about new features? That is not an update to Lightroom 5.7.1. If that is the noticed you are reading, it is telling you that there is a new version of Lightroom. The new version is a paid update. If you're not interested, notice in the lower left-hand corner there is a button you click to ignore those messages.
It says a Lightroom Update is available. Problem is I have already installed the 5.7.1 update. If I click Ignore These Updates will it ignore all future updates? If I click Download it takes me to the CC window where it wants me to download the CC version. Shouldn't the system know I have already installed the 5.7.1 update and not keep telling me it is available?
The text in the white box is misleading. Current version: 5.7.1 is referring to what you have installed.
A better text would be: You have 5.7.1 installed. You can ugrade to version 6/CC.
The text also leads you to believe that this an update, but it's an upgrade.
As for version 5, there will be no further updates, so unless you want to upgrade to LR6, you can click Ignore.
Frabjous! I plan to upgrade to 6 - permanent version - in the near future. Thanks.