confusion
Using Jamroom
You can modify the header.tpl for your skin in the ACP > Skins > YOUR-ACTIVE-SKIN > Templates section. You can also upload a new logo image via the Images tab for YOUR-ACTIVE-SKIN as well and modify your header_menu_desktop.tpl and header_menu_mobile.tpl files as well.
Or you can modify the templates directly by using a FTP client to download the skins/YOUR-ACTIVE-SKIN/header.tpl, header_menu_desktop.tpl,header_menu_mobile.tpl and your skins/YOUR-ACTIVE-SKIN/img/logo.png templates and files.
However... If you modify the templates directly, you may want to clone the skin first. This way updates to the skin do not overwrite your modifications.
You can clone a skin via the ACP > Site Tools > Developer Tools > Tools > Clone Skin. Note: you'll need the Develper Module installed.
Hope this helps!