Basic: How to delete an iOS app or game from your iPad or iPhone
Okay, let's start with the basic deletion process. (This is for the beginners. If you know how this works, skip ahead to the next step.)
Start your iPhone or iPad and go to the Home screen (press the Home button below the screen, or touch all five fingers to the screen and draw them inwards like a claw.) Find the icon for the app you want to delete, and press and hold it for a few seconds. It (and all the other icons on the screen) will start to wobble gently, and a small cross will appear in a grey circle by each. Tap the cross, then confirm you want to delete the app.
How to delete an iOS app from iTunes on your Mac
If you sync your iPhone or iPad with a Mac on a regular basis, you'll need to remove the app from the Mac too. Open iTunes, make sure you're in the library section (if you're in the iTunes Store, click on Library at the top right of the screen), then select Apps from the dropdown menu at the top left. Find the icon of the app you want rid of, right-click it and select Delete.
To get rid of any other pre-installed app
is rather impossible, because apple does not allow that, but a workaround may be to move the unwanted icons to a map you might call for instance "apple stuff".
To organise apps into folders, press and hold the icon for one of them until it starts wobbling, then drag it on to the second app you want to be in the folder. iOS will automatically generate a title for the folder based on the apps' descriptions, but if you tap this name you can rename it into "apple stuff".
Place this map on a screen very much to the right and you might almost forget it is there.
If you still want to free up more space, have a look here:
How to Free Up Space on an iPhone or iPad
Good luck !!