To remove annoying ads from apps you use online, with your finger, tap on the ad, keep holding and swipe it up. This works on most ads, but not all. Especially the ones placed in the bottom.
To remove ads in apps that you don't need to be online while using (like games for exp.), just turn off your internet connection (wifi and 3G). Or just turn on the airplane mode.
To really get rid of ads. You have to jailbreak your phone and install iAdKiller. You can follow the steps using this link bit.ly/HxcCYX
And of course, you can always purchase the apps :)
The creator of this guide has not included tools