If they are Subscribed here on STEAM -> The easiest way to unsubscribe from them is:

Go Here:

Steam Workshop

Over on the right-side you will see: (among other menu options:

Your Favorites
Subscribed Items

Click on: SUBSCRIBED ITEMS

The list of Steam Mods you subscribed too will be shown here.
Simply Click on UNSUBSCRIBE BUTTON on the right of the Mod Title.

Part 1 - Done.

Part 2:

Click on the SKYRIM Icon to launch your Skyrim game -> NOT THE SKSE ICON.

Here you will see:

PLAY

OPTIONS

DATA FILES <---

TECH SUPPORT

EXIT.

Click on the DATA FILES and you will see the STEAM MODS and they will be listed by:

Mod Title/FILE NAME .............. SUBSCRIBED ....
CLAMS GIVE PEARLS ---------- YES.

HIGHLIGHT the Mod you wish to remove/delete, by clicking on it w/your mouse.

Then Click the bottom LEFT Button - DELETE SELECTED.

You will get a confirmation, that this is what you want to do.

Then when you are all done ... close the Skyrim Window ... then wait 1 or so minutes and re-open. Then let it SYNC with Steam - you will see this happening in the bottom Center/Right .. when it is ALL DONE .. open again the DATA FILES option to confirm the mods are gone.

If by some chance they are not - just repeat the above and it should clear the next time you repeat the above.

Some have found - me included, that it might take 2 times to get all the mods removed.

Also verify that you UNSUB'd from these in your Subscribe Mods in Steam Skyrim Workshop link above.

... Jj ...

Thanks so much for the awesome explanation. Really sorry if this was explained already as I am sure it was. I was searching for a while and I flat out gave up, Again, thanks for taking the time to write it for me. Take care Jj

I tried to do this but for some reason after i unsubscribed all my mods and went to delete them they wont disappear from my data files list. Could this be a conflict with nexus mod manager?

NMM still can load the downloaded mods, switch to the plugins tab of it and turn off each mod you don't want.