I've had trouble with installing on an external hard drive like I planned to, so I've decided it would be better just to set up a dual boot on my system. I've been searching to make sure I do it correctly, but I am running into some differences between my system and the ones being described and want to make sure it won't cause me any problems. I'm running a windows 8 that I had upgraded form 7, so it wouldn't be a secure boot if I'm correct on that since it wasn't preinstalled. Most of what I am coming across talks about using a preinstalled Windows 8 so I wanted to make sure this won't cause me any problems installing it as normal.
The other problem I'm running into is everything I am finding talks about installing on a UEFI enabled system, and I'm running a legacy bios at the moment. Is that going to cause a problem? If so, is there a way I can make my machine a UEFI enabled system so that i don't run into these problems?

The computer I have is a Dell Inspiron N5040 laptop if that is needed, and if necessary I can give you whatever specs you may need.

If you need any more information from me on my machine or anything, just let me know

I've possible, I'd also like to know how I would go about removing Ubuntu if I decide I don't like it (though I doubt that would be the case) or if I for some reason can't get it to work. I've found some guides that require the original windows CD but I don't have that, and I've found some about using EasyBCD but from what I've seen it doesn't have a Windows 8 option.