What's wrong with my storage?

I have an iPhone 4s. I want to download IOS8 but it requires at least 4.6 GB of storage. My storage plan sucks *** so i only had 6 GB to begin with, so i deleted all of my apps, messages, music, photos, videos, voice memos, and every single one of my contacts. As of right now i still cease to have one app that i can physically delete. Yet in my usage settings i only have 3.5 GB of data that i'm able to use and some of the apps are still taking up storage. I even bought 200 GB of iCloud storage but nothing is working. I'm completely unable to delete anything else! What do i do?

The minimum size of a 4s is 8GB, so don't know where you get 6 from.
If you go to the storage settings you should see a section called Other. There's usually stuff in there. Dropbox sticks things in it, and a few other apps as temporary storage. ICloud storage won't help.

Use your computer and download iTunes for it if you haven't done so already. The hook up your iPhone to the computer a register it to iTunes. ITunes should tell you that it has detected an update for the phones OS and did you want to download it, say yes, it may also ask if you'd like to backup your iPhone before updating it. ANSWER YES.
When it is done with the backup, it will go through the update process for iOS8.