I was just wondering how can I change Arena's regular screen into fullscreen, I have the free version Bethesda is offering in the Elder Scrolls site, since it's the floppy version, I'm not sure if this could be done, but any advice/suggestion/solution will be greatly appreciated. Thank you.

If you're running it in DosBox, then reading the sticky would do you well.

Thanks for your help. =)

If you created a dosbox config file for the game, you can go into it and there will be a command line you can edit so that the game will open in full screen. Check the sticky for how to create said file and a shortcut so it's usable.