I m having a hard time hitting barr chords on guitar. Any advise?

First things first.  Bring the guitar to a luthier or guitar technician to check the setup.  Key items to check and adjust in this order are (1) Neck relief, the very, very slight forward bow of the fretboard; (2) String heights at the nut (frequently much too high); (3) String heights over the 12th fret.wire.  These preliminaries are done in just a minute or two, nearly always at no charge.

If the guitar is in good adjustment, and you play a steel-string acoustic, consider switching to a lighter string gauge, say 11-to-52.

If you play electric, there's no good reason to use lighter than a 10-to-46 set.

If the guitar is properly set up and the strings aren't too heavy, the difficulty could be due to your technique.  Schedule a couple of lessons with a guitar teacher who has some classical guitar background.

I met a young fellow in a music store about a year ago, who mentioned that he could not play barre chords (what you're having trouble with) due to small hands.  I knew that couldn't be the cause, as my hands are even smaller, and I've played barre chords since the first few minutes of learning guitar.  After I'd corrected the angles (fore&aft and lateral) he held the guitar and changed his thumb placement, he played an F barre for the first time.

Regardless that a lot of people disparage "technique", good basic technique is essential.  You need a teacher who knows and practises it.