Yes, you can. If you purchase VIP when you have already purchased "NO Ads" then your VIP will take over the "NO Ads". Once the VIP expires or you cancel it, you can use the remaining of your "NO Ads".

 
For example:  A User purchases "NO Ads" for 30 days. On day 5, the user upgrades to VIP for 30 days.
The remaining "NO Ads" status becomes extended by the VIP duration, meaning the user has 25 days of "NO Ads" if/when the VIP expires