I currently play on my epiphone les paul with 11's in standard with minor buzz on the second fret of the e string.

i want to change the gauge of the strings down to 9's and i need to know whtether i need to adjust my truss rod.

and if so which way do i need to turn it?

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99% chance you will - you'll have to turn it left to relieve the neck. You'll probably be able to lower your action a little too (with the bridge). Just put them on and see, if they lay against the neck, take it out with the truss rod (1/8-1/4 turn at a time, do it slooooowly), then adjust the action to suit. That's a pretty big jump, from 11's to 9's.