Changing the label on links
This is highly dependant on how the fields and templates are set up.

You don't say how you are creating the link. Craft makes no assumptions as to how you are going to be entering content. It's entirely down to the developer to set up the fields and templates according to your needs.

Do you have a text field specifically for entering the link? If there is no accompanying field to add a title then it's most likely you will need to add one and then modify the template to output that field in the title attribute of the link.

If you are adding a link within a Rich Text field then you should be able to edit it from within there. Though if this were the case I don't know why you would have a default value being used.

Either way, it should be a very minor task for a developer to fix.