Its easy to remove the App completely from your theme

Step 1: Go to Settings, then go to Apps. Log in your store with the store owner's account, then go to the Settings field in the bottom right. ...

Step 2: Click on the "Apps & Sales Channel Tab" from the settings page

Step 3: Find "Ecomartists - Drawing on Demand" App and click "Uninstall"

Step 1: Click "Online Store" on sidebar

Step 2: Choose themes

Step 3: Find your Published Theme and click "Edit Code"

Step 4: Under "Snippets" Find "ecomartists-upload.liquid"

Step 5: Press the trash can to delete

Step 6: Find "theme.liquid" under layout section

Step 7: Scroll to the bottom and find "{% include 'ecomartists-upload' %}"

Step 8: Delete and Save theme.liquid

Congrats you have successfully removed Ecomartists app and all its components.