You are certainly not alone with this problem – as low-price routers are usually simply unable to break through some thick walls.
Hence the first piece of advice: try not to place the router in the corner room, place it closer to the middle of the apartment, for example, somewhere in the corridor. Yes, perhaps you will have some inconvenience trying to hide the wire, but it's worth it. Also keep in mind that it is better to place the router as high as possible. Therefore, the best place for that is right under the ceiling.
Also a good idea is to take a look at the device, the way it is loading and keeping temperature. Overheating may affect its performance, so do not place the router in a remote place and close to the heat sources. A CPU usage can be estimated by entering the admin panel of the router (usually the CPU is overloaded in low-end models).
Try to update the firmware of your router; usually it is available on the manufacturer's website along with the instructions on updating. If possible, try somebody’s more modern router and see if the situation changes for the better.
If the purchase of a new modern router is not included in your financial planning, try to use a signal repeater. These devices are much cheaper than routers, and thus greatly expand the coverage area. I recommend choosing the model TL-WA854RE from TP-LINK.
It can operate in two modes - easily increasing the coverage of your network, and creating a new network based on your already existing one with its own username and password. The setup is very easy and even beginners shouldn’t have any problems with that.
If you have any further questions, please do not hesitate to contact our help desk!