How do I sync contacts which I scan into cardscan to salesforce?
How do I sync single contacts I add to outlook to salesforce?
How do I add an updated email to a lead and have the previous one deleted or updated?
How do I sync my outlook calendar to salesforce?
If you are using Office 2007 or later, you need to use Salesforce for Microsoft Outlook.
Both can be found by going into your instance, clicking on your name, then Setup, then on the left under My Personal Information, then Desktop Integration, then Salesforce for Outlook. There is a link on the next page if you need to use Connector for Microsoft Outlook.
Each app has a great help system which can walk you through the process for both your first and third question. Alternatively, open up the help & training area, type the question and it'll pull up the exact instructions for which app you search on/need.
The app will also let you associate an email to the object in question, but it does not automatically delete what was there prior.