You can, but only in a few circumstances.
- If there is a source in the template email that is sent to the lead dropbox, it can set the source.
- If a lead is being imported from a file, the source can be set in the file and used.
- If a lead was manually added by you, you can choose the source when adding the contact.
- In Zapier, the lead source can be set manually or automatically. It's one of the fields you can setup when configuring a zap.
- When you are building landing pages or squeeze pages, you can set the source name at the time you create the page.
Depending on how the source was assigned to the lead, you can change it by hand if necessary. When the system assigns a source automatically, it cannot be changed.
To edit the source (if available):
First, open a lead/contact. On the left hand details panel, expand the 'More Details' section.
Then, scroll down to the 'Referral Source' section, and click on the source name to change it. If you cannot click on the source name to change it, then the source cannot be edited.