RESOLUTION
By default, upload max image size in SiteStudio set to 524288 bytes.To increase max image size please add MAX_IMAGE_SIZE variable in /hsphere/shared/SiteStudio/psoft_config/masonry.properties file and set size in byte.
After this change changing, restart your H-Sphere CP.
For example:
MAX_IMAGE_SIZE = 3000000
This means that now you can upload image with maximum size 3 000 000 byte (3 Mb).