1. If the plugins came with an installer, run it again and it should ask you to uninstall it. Check the installed programs list in the control panel and see if it lists New Blue as an entry.
2. See where the corresponding New Blue files are downloaded and delete them. This should be where the other effects plugins are installed. on my Windows machine, they are at "C:\Program Files\Adobe\Adobe Premiere Elements 11\Plug-ins" Some are inside "Common" folder, some within "en_US\AEFilters" folder. I don't know why there are two separate folders, but there you go.
3. Some releases ago, there was a mention by Adobe folks of the loaded plugins in the registry causing crashes (I think PrE v8). I see a plugin cache on my machine at HKEY_CURRENT_USER\Software\Adobe\Premiere Elements\11.0\PluginCache.64. I also see that on deleting this, it gets regenerated the next time PrE is launched. So seems safe to me. I am able to apply effects even after this little prank.
The installer, if available should be the safest and easiest and hence the first option to attempt.