Note that changing texts is almost always language specific. If you make a more complete mod and plan to distribute it, you might want to package the texts separately (as my_mod-texts.pak for example) to allow an easier localization.
The text file for creature names is found in Text\Game\Creatures\*Town*\*Creature*.txt so just change it with notepad, save, and play.
Same as 4.1, but the files are found here: Text\Game\Heroes\Persons\*Town*\*Hero*\Name.txt
The files are in Text\Game\Creatures\*Town*\*Creature*Description.txt so change, save, and play. To change the Ability Description (not the ability, but what’s written when you right click a monster) the files are in Text\Game\Creatures\*Town*\*Creature*Abilities.txt so again, change, save, and play.
You probably got the idea. Files in Text\Game\Heroes\Persons\*Town*\*Hero*\Bio.txt