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.
WordPress uses widgets to display content in the sidebar. To change widgets, open the dashboard and go to Appearance > Widgets. From here, you can add, remove, or reorder widgets by dragging and dropping, as well as customize the appearance of the sidebar using individual widget options.
Depending on your theme, you may also find additional sidebar customization options, such as colors, sidebar width, etc., under Appearance > Customize > Sidebar.
