How do I change the "From" address in site emails?
The From address of site emails sent via newsletters, form submissions, and other site communications will be the main site administrative email address, set by visiting Admin > Site. It is recommended to use a general, organization-wide email address as your main site address, such as "firstname.lastname@example.org".
The Name associated with the address will be the Site Name, also set in the Admin tab. Since this name is likely used in the site templates to designate the name of your organization, it is not recommended to change the Site Name to "Webmaster", etc.
For more on Newsletters, see this resource.
For more on Forms, see this resource.