First you need to install the widget (follow the instructions here: https://www.ads-software.com/plugins/wp-instagram-widget/installation/ or install the plugin from within WordPress by searching for “WP Instagram Widget” on the “Plugins -> Add new” screen).
Once installed and activated you should be able to manage the footer of your website via “Appearance -> Widgets”. If your theme does not support sidebars/widgets it you may need to modify your theme’s code (if that is the case then post back).
You can find a guide on managing widgets here: https://codex.www.ads-software.com/WordPress_Widgets#Displaying_Widgets
You will then simply drag the Twitter widget away from your footer and drag the “Instagram Widget” into the footer. You will need to add your username to the widget options and choose the number of photos you wish to show.
