It’s not a complicated or difficult thing to do. Pay attention as we go along, because if you do it wrong, you can ruin some functionality and botch data sets .
First, note that this is only available in contact manager, group, professional developer and database.com editions. (Standard objects are not available in the database.com version, so this tutorial doesn’t actually apply to that edition).
You must have the permission ‘customize application’ in order to do this. If you do not have it, contact your administrator and request this permission before you continue, or it simply will not work.
Go to ‘Setup,’ click ‘Customize’. Select the object or field you want to configure.
Next, click Fields->Set History Tracking.
You will be presented with a checkbox that shows the various forms of data and the choice of ‘history’ you may track: such as account history, lead history etc.
You may combine up to twenty data fields within the object you want to choose. Choose at least one because if you choose none, you’ll be bounced back to your dashboard, or your browser could be stuck in an infinite loop until you refresh. (Salesforce is addressing that issue).
Finally, click ‘Save’ to apply your change.
Congratulations, you have enabled field history for standard objects in Salesforce.