It because you make scene before more lighter for ram. Close all not needed programs, browser etc. Maybe you insert objects with displacement, you can try to disable it, convert textures to jpg and reduce resolution if possible. Do not use lightmix and render elements. There is few option in corona what can reduce ram usage, and you can try to turn off VFB, setup save or autosave of rendering crx, this is also may reduce usage of ram. Restart 3ds max before rendering.