In PO (Pokemon Online), to edit EVs and IVs, simply go to the TEAM tab on the Teambuilder. For EVs choose your Pokemon and it's base stats for that level will appear. Click the white box across from the stat you're hoping to build upon. IVs are already set up to 31 but to change them click on the box below you Pokemon that says ADVANCED. Choose either SIDE WINDOW or NEW WINDOW (you'll see what they do when they come-up. On the window will be many added options such as Hidden Power, Abilities, Shininess, Happiness, Gender, and in this case IVs. Select the IV number you want, they're already set as high as possible.
I hope this helped! BTW, I play too. Whats your PO name and what server have you been using? I'm Robo Pika on the Battle Tower.