Hoang,
I need a liitle more information so I can understand how this situation happened.
Are you using the P-CAD to PADS translator? Is this a SMD or PTH library part?
If you want to know how to flip pads from Bottom to Top, you use the PADS Decal Editor > Setup > Padstacks > Change the Bottom value to zero and the Top Value to whatever the Bottom value was.
Let me know if you need me to post picture graphics on how to do this.
Tom