How to pay tax, before or after uploading itr

you have to follow https://www.incometaxindia.gov.in/home.asp  link and there will be a tab for pay taxes online there you have to select your bank and fill the details needed then you will be generated a reciept and you have to fill the BSR code, date and challan serial no. in the ITR return and then again click on calculate tax then generate XML on https://incometaxindiaefiling.gov.in by loging into your a/c

Pay the tax payable, and mention the challan details in the revised return and then upload. 

If Tax liability exceeds TDS deduction, then one must pay self-assessment tax. This can be paid via the website itself and need not go to the IT office. After paying self-assessment tax, the website will generate a payment challan or a receipt, in which details of the payment shall be given. This detail will have to be entered in the ITR confirming that you have paid balance tax liability. So first pay self-assessment tax, then file ITR.