Do you have FTP access to your website? You'll need:

• A FTP host address such as ftp.mydomain.com plus a username and a password to access that address with a "FTP client" software. The FTP host address and the username and password is something your web hosting provider should have given you. It's impossible to know that without being told. If you have a web hosting control panel such as Cpanel, there's probably a FTP section in that panel where you can set up an FTP account with username and password. The FTP host address should also be listed somewhere in that section of the control panel
• A "FTP client software" such as https://www.ohloh.net/projects/filez...in32-setup.exe

After you installed Filezilla start the program, choose File -> Site Manager -> New Site -> Optional: Type a name such "My Blog XY" while "New Site" is highlighted -> Put this info into the window

Host: The FTP Host address (sometimes called "host name" or just "host") that your web hosting provider gave you or that you saw listed inside the FTP section of your web hosting control panel
Port: Leave empty
Servertype: FTP - File Transfer Protocol
Logontype: Normal
User: The FTP user name (may be different from your web control panel user name) that the web hosting Provider gave you, or that you created yourself inside the web control panel
Password: The FTP password (may be different from your web control panel password) that the web hosting provider gave you, or that you created yourself inside the web control panel

Click connect, and after a few second you should see the harddrive contents of your local computer in the left window, and the harddrive contents of the web hosting server in the right window.

In the right window (the one showing the contents on the web hosting server) click into the folder name resembling your domain name, probably either "yourdomain" or "yourdomain.com". After you're inside that directory you should see /wp-content/. Inside that should be /themes/. Inside that /atahualpa/ or /atahualpa2/. Inside that /images/ and inside that /header/. So the total path should be something like /yourdomain.com/wp-content/themes/atahualpa2/images/header/. Once your in that directory in the right window, find your images on your local computer in the left window. Then drag and drop the image(s) with the mouse from the left window (your computer) into the right window (the web hosting server).