Just follow these steps:

1) Click My Account at the bottom right of the client.
2) Click the P2P Transfer button.
3) Enter the screen name of the player you’re sending funds to. Remember, they must be a player at the same site (that means if they play on the Winning Poker Network but at a different site, it won’t work).

4) Enter the amount you want to transfer, keeping in mind your displayed limits. And if you want, include a few details in Notes.
5) Click Transfer to see a summary of what you’re about to do.
6) If everything looks good, click Confirm.

Your transfer should show up under the Pending tab. And when the transfer’s done, which usually takes about 5 minutes, you’ll see the details under the Summary tab.