Joomla comes with a built-in text editor: TinyMCE.
Although this is OK for many users, the need to change it to something more advanced may arise. When installed, you need to make sure that the editor is selected as the default editor.
I'll show you how to do that.
Some users have trouble setting the default editor and having it display correctly when users are editing articles - I'll explain why below.
I recommend JCE
I usually recommend JCE as a replacement editor when asked. I like the way JCE is made, and the fact that you can install plug-ins easily to accommodate different needs. You can also create different user groups. This means you can show different editor layouts and functionality to different users. Very useful if you have users with varying computer knowledge. JCE itself is free. To download the plug-ins you need to subscribe, at a price I find reasonable.
Global Configuration
When the text editor has been installed you need to make sure it will appear when editing articles. The first step is to go to 'Global Configuration' and set the new editor (JCE, for instance) as default editor.
This might be all that is to it, but I encourage you to check one more thing if the new editor does not appear in article editing mode.
User Setup
Go to 'User Manager' and into your user setup. Some admins have the habit of setting the user editor specifically for each user in this screen. This is not good to do if there's no specific reason to do it. If the editor is set to TinyMCE on a user, this setting will override the Global setting. As always, if you don't need specific settings somewhere, please leave it at '-Select Editor-'. This way, you can change the editor once and it will work for all users. Imagine the horror of doing manual change on, worst case, hundreds of users...
If someone for some reason really needs a different editor, set this in the specific user settings and everybody's happy.