Where do u go to upgrade ur wepons,

You buy weapon mods from traders. They're pretty easy to spot with names like "Varmint Rifle Night Scope". Then you add them to your weapons in the inventory. You'll see the 'mods' option light up when you have one for the weapon.

Bring up the weapon on your pip boy and use the LB or RB i forget, and it will list whatever upgrades are available for that weapon. Select the upgrade and its done.

You can also highlight the weapon in your Pip and click X as well I believe.

I dont get the option to upgrade. What am I doing wrong?

Are you sure you have an upgrade for the weapon selected? If you have a 9mm pistol scope you cannot upgrade it to a .357 pistol.

I have upgrades for multiple weapons but I cant seem to upgrade any of them. Barrels, scopes, silencers, nothing seems to let me upgrade.

Not sure then....on the pc I open my inventory, select a gun, press the 'x' key and any available upgrades are shown and I click on the one I want, its added to the gun. Dunno about consols...

Thanks. I will check back later to see if anyone has an answer.