If a person had more than one name, we recommend that you pick one as the name which you intend to use to identify the person, and enter that in the field of the Main tab of the Property Box as described in How to Enter a Person's Name.
If the person had two or more names, you can enter all alternative names in the Names/Titles dialog for the person in question. To access this dialog, open the person's record in the Property Box, and click on the more... text link, to the right of the Name field in the Main tab.
The advice in How to Enter a Person's Name about how to enter names, still applies when names are entered in the Names/Titles dialog.
Titles can also be added in the Names/Titles dialog. Click on the button and then choose from the dropdown menu. You can add also add titles in the Facts tab of the Property Box. It doesn't matter which you choose. If you add them in the Facts tab, you will be able to see them in the Names/Titles dialog, and vice versa. You will find though that you can enter more details about titles in the Facts - even if you didn't originally add them there.
There is no limit to the number of names or titles that a person can have.
Nicknames can also be entered in the Names/Titles dialog.
It sometimes happens that a person was not usually known by their first name. For example, if Jean Clare Smiley was always known as Clare by everyone who knew her, enter 'Clare' in the field. If the person was always known by their first name you should leave the field blank, as this is the default. If Jean Clare Smiley was always known as Jean Clare, enter 'Jean Clare' in the field.
If the person had a name prefix (such as Dr, Sir, Colonel, etc), these should be entered in the field. If the person had a name suffix (e.g. Jr), these should be entered in the field.
Do not confuse titles (such as Lord Dittington) with name prefixes (such as Dr).
If you wish to record an event of the person changing their name, you would need to create 'Name Change' as a custom event, and use that to record the name change. See How to Create a Custom Fact (Event or Attribute).
See also How to Record a Woman's Married Name.