There are a few ways to remove a custom indicator that you've installed in NinjaTrader 8. Which method may depend on how the indicator was installed or what features it has.
If you try to remove an indicator that's in use, NinjaTrader may give you a warning, and in that case, make sure to close any open charts that may be using the indicator. One way to do this is to close the current workspace and open a new one.
The first thing to try is remove it using the NinjaTrader Control Panel's menu, by selecting Tools / Remove NinjaScript Assembly. Choose the indicator that you want to remove from the list that appears. Once the indicator is removed, you will no longer see it in the list of indicators in the popup.
Some installed custom indicators will not appear in the list that's described in the steps above. In that case, you'll need to remove it manually. This can be done in several ways, and here are a couple of ways to try:
1. Using the Ninjascript Editor: Open the Ninjascript editor using the New / NinjaScript Editor menu command from the NinjaTrader Control Panel. This will open the editor, and at the right, double-click on the Indicators heading to expand the list of all indicators. Locate the indicator you want to remove, select it, then click your keyboard's Delete key. You'll be prompted to confirm the removal, and clicking Yes will complete the removal.
2. If the NinjaScript editor is not available to you, or the above procedure did not work, you can manually remove an indicator by finding it within the NinjaTrader file folders. First, make sure that NinjaTrader is closed before attempting to delete the files. You will normally find custom indicators in your My Documents folder, in the directory path, NinjaTrader 8\bin\Custom. In that directory, locate the indicator you want to remove. There may be more than one file with the name of the indicator - NinjaTrader indicators typically have files ending in both .cs and .dll. For example, if the indicator you wanted to remove is called "test", you would delete both test.cs and test.dll. If you want to later restore these files, you can cut/paste them elsewhere temporarily until they're needed again, where you can just add them back to the same folder you removed them from. It's possible that indicators are stored in other subfolders in the My Documents folder, so if they're not appearing in the bin\Custom folder, look around the directory structure to see if you can locate the indicator files for removal.
If none of these approaches work for you, you can contact NinjaTrader support for assistance in removing the indicators.