If roms stored text in ordinary ASCII format, you'd be able to hack text using plain old Notepad. Most don't, so you need a program designed to convert rom text to ordinary text you can see and change, and vice versa. While starting out, I recommend Necrosaro's Thingy.
Whatever program you're using, it needs to know how to convert between rom text and normal text. That's where a table file comes in. A table file is a list of conversions. In the last section, we found out that in Zelda 2, EB=R, DE=E, and so on. You can start your table file already. Make a text file and type in
EB=R DE=E ED=T EE=U E7=N
Actually, you can fill in the rest of the alphabet too. If DE represents "E", DA must represent "A". Fill in the rest of the table, with one line for each conversion. If you want to save yourself some typing, check out my Table Maker utility.
Now that you've got a table with the whole alphabet in it, you can use Thingy or my script tools. Run Thingy and give it your Zelda 2 rom and the table file you just made. Jump to E76Ch and you should see text, which you can easily edit through Thingy.
There are still some things missing from your table, though. You're missing punctuation, for one thing. Also, the rom uses certain special characters to tell it when to start a new line, end the message, etc. By looking through the rom in Thingy and comparing what you see with what the game displays, you can figure out that F4 is a space, FD is a line break, CF is a period, and FF is a message end.
Now for a change of pace. You might have fun changing the font the game uses, especially if the original font is hard to read (a la FF1 or Faxanadu). Also, if you're trying to translate a game into another language, you'll probably need to change the font.
I recommend you use SnowBro's Tile Layer for your graphics hacking. It's pretty self-explanatory. Go get it and start it with your rom. Scroll down until you find the font, or whatever you want to change, and go crazy. La! That's that.
SnowBro's home page seems to have vanished, but Tile Layer can be found on the Translation Utilities page at Zophar's Domain.