To upload a new logo, log in to WordPress and navigate to Appearance > Customize. Depending on your WordPress theme, you may see a "Branding" or "Header" section where you should find an option to upload a custom logo.
Alternatively, if your theme uses a custom theme panel instead of the WordPress customizer, simply select your theme panel from the main dashboard, find the Branding/Header section, and you will find a logo option.
