So I downloaded the freeciv .deb package, but when I began to install it, I realized how much space it would take up and then decided against it. Problem is, that 26-mb file is still on my system, eating up space. Where do I find it and how do I get rid of it?

There are three "drives" on your tablet: the internal memory where all your apps/settings go and where you can possibly store files in the pre-defined directory layout , the internal card which is 2 GB on an N810 and variable on an N800 depending what card you have and the external card which varies on both tablets.

If you finished the download and just never installed it yet, you have to remember where you put it (since you would have had to have picked a spot ) and go in with the file manager to delete it. If you went with the default, it is most likely sitting in the "Documents" directory.

If you installed it and want to get rid of it, go into the Application manager and tap on Show installed applications and when you tap on an instaled app it give you the option to delete it.

Start here if you know the file's name. Then try googling something like

remove OR delete "Linux command"

(It's possible nothing was ever installed or even saved if you cancelled parttway through.)

another possibility is that it got cached by apt. if you have root access in place, enter the command 'apt-get clean' to clear said cache.

Ok, so how do I get root access in this place? I put the command in xterm and it's asking for a password. I haven't changed anything, so if there's a default password then that's it. What is it?

http://www.gronmayer.com/it/

search for becomeroot or easyroot.
note however that the page will only install the repository that holds that package, you will have to look it up using app manager afterwards iirc.

then its one of these:

if you selected becomeroot: sudo gainroot

if you selected easyroot: root