What can i use to clean the inside of my 50 mm lens?

I have a 50 mm lens. For a Nikon EM, but after much cleaning of the outer part of the lens it seems to still be dirty, i'm not sure if its on the inside of the lens? Or perhaps i need to change cleaning liquid? I'm very new to this camera lens stuff so some information would be much appreciated thanks.

You won't be able to clean the inside of your lens.

You'll have to have it professionally cleaned or, better yet, just buy a new lens.

Older MF 50 1.8s are inexpensive.

Don't
Take the lens to a camera repair shop that can disassemble and clean the lens and the put it back together properly.

Since your lens is probably one of the E model lenses, it may cost more to clean than it is worth