Always back up your original partitions before writing new data to the flash memory. To help you get started with the right files, let me know:
That 512MB of RAM is the reason you cannot run a standard Android ROM (lineageOS is virtually impossible here—the system would crash on boot). The community has instead focused on lightweight Windows-on-ARM and minimalist Linux. Nokia Lumia 520 Custom Rom
After writing the image, reboot. If the screen stays black, hold Volume Down + Power for 15 seconds. You must re-flash the EmmcBoot.bin via QPST (Qualcomm Product Support Tool) if Windows doesn't detect. Always back up your original partitions before writing