To upload an image to Contensis, it must be below 1024kb. If your image is too big, use TinyJPG or TinyPNG to compress the file, depending on file type.
Editing and resizing images can be done within Contensis by clicking on the image in the 'Project Explorer' and chosing 'Create Variation'.
If a more detailed editing process is needed, use Photopea or Canva to edit the image to the required specifications.