@7bo0d
What is the country version of the router, it is EU or US, or another version? You can find that on the router bottom sticker just beside the model number.
Then try to find the latest firmware version for the hardware. If it's an EU version, you can get and download the latest firmware from the global website as this one. If it's a US version, then here is the latest version.
If it's not EU or US, then find the latest firmware from the local website.
Here is the guide that shows you how to upgrade the firmware.