First of all, on the company form view, you can change the logo, the tagline, the bank numbers... this is automatically changing the header/footer of the reports.

If you need more customization, you can * edit your user to enable the 'technical features' option * go back in the company form view and there should be a new tab with header/footer currently used by the system. The syntax is rml, you can edit and use the 'preview header/footer' button to see your changes.

But beware, as this option says: this is a bit technical (rml syntax is not the easiest). I'd suggest to keep on using the generic report header/footer as much as possible and thus only change the information on the company form view.