Hi Praveen,
It depends a bit on how proficient you were in PHP when you last used, but as it's only been a couple of years I don't think you can erase all memories you have of using it (short of some trial and error with your head and a hammer but that's a bit extreme).
It's not a very complex language so I would say the best thing would to just do a couple of small fun projects, for yourself or someone else, and it will come back to you, then just use something like php.net or w3schools.com to fill in the gaps.
Another option would be to buy a book, such as
Beginning PHP6 or
Professional PHP6 and work through it as if you were a complete beginner, but skim through the bits you really remember or you'll probably get bored.
HTH
Phil