duplicate photo libraries

I have two photo libraries now that I updated to 10.13.3 mac OS High Sierra. How do i get rid of one of them?

What do the libraries look like in the Finder?

if you look at your Pictures folder in List view, you can see the "Kind".

A Photos Library will have a rainbow flower icon, the filename extension ".photoslibrary", if the extension is shown, and the kind will be "Photos Library".

An iPhoto Library for iPhoto 9.6.1 will be showing an icon with a pink flower and kind "Photo Library" (without the "s").

If you just migrated an iPhoto Library or Aperture Library to Photos, the original library will have the filename extensionc".migratedphotolibrary" or ".migratedaplibrary". The original library will be sharing the image files with the Photos library by hard links and not use much extra storage, even if the file size of the library is as large as the file size of the Photos Library.

Photos saves disk space by sharing images with your iPhoto or Aperture libraries - Apple Support

See this complete article Designate a System Photo Library in Photos - Apple Support

move it to the system trash and empty the trash

BUT

I doubt that you actually have two duplicate libraries and I suggest that you be very careful about what you are doing or you are likely to make a mistake and lose photos

LN