is it the primary partition? if so then you will have to reinstall the whole system. if it was on a separate drive you just set the win 8 drive as primary and repair install it when your given the options of where to install it you can then delete the win 7 partition then slect repair install for windows 8. this will adjust the boot sequence and make win 8 the primary o.s.
Drive C : Installed Win 7 in 2010 (50GB)
Drive D : Data (190 GB)
Drive E : More Data (134GB)
Drive F : Win 8 Installed 4 months back as a fresh Install (90 GB) For This I Shrank The Drive E From 220 to 134 GB
In Device Manager Wizard Shows
Drive C : System,Active, Primary partition.
Drive D,E : Logical Drive.
Drive F : BOOT,Page File, Crash Dump,Logical Drive
So You Are Sure I have To Do A Clean Install There Is No Way Around It Or Rather Temporary Fix Like Deleting Everything On Drive C Except "Boot Files Windows folders Stuff Like That" To Recover Some What 30GB/50GB From The Drive.
I Don't Boot Into Win7 So I Don't Require It.
Get an external drive that can store all the data you want to store (I can go through things like Steam games, my docs, etc with you if you need)
Use the Windows 8 install to remove all the partitions on your drive, then install W8 in a single partition. W8 will create the extra partition it needs and you will have the best setup for your PC to run smoothly.
If you do not have an external drive, spend the £30 - £40 odd it will take to get one. You will not regret it!
Another choice for you is to purcahse an SSD to use as a boot drive and then keep your data on the older normal Hard Drive.
If you choose that option, again let me kow - I can point you in the direction of a great install guide for W7 and W8 on SSD.
Also check for hibernation or system restore files. (you can remove the restore files easy with CCleaner). Also uninstall any unwanted software or games, sometimes they will take up quite a bit of space. Make sure you are in Windows 7 when doing these operations.
like i said if you have it on a different drive it would be an easy enough fix that would take 20 mins. but because there all on 1 drive you cant remove 1 without affecting the other. so all you can do is back up your personal data and format the drive.
aslo its better to have less than 2 partitions on a drive as each subsiquent partition will slow the drives response by 10%. the way you have it setup the drive is about half as fast as it should be and you will be lucky to get reads and writes in the 40-60MBps region when it should be closer to 90-120 (depending on the drive). so consider dumping 2 of the partitions. you really should see a difference in drive speeds.