Please set max_upload_filesize and post_max_size values on your server to the value more than the size of image you want to upload.
Please set 16M to both the variables once and then upload the image.
once you install the QloApps it creates a fontend as to provide a fully functioning hotel reservation system. To edit the frontend you can create a new theme or edit the default theme "hotel-reservation-theme"
QloApps is based on Prestashop, please follow their doc to understand how theme works.