First, ensure the speed from your ISP by connecting a PC directly to the modem bypassing the router via cable and run speed tests. Assuming all is good... Try moving the router as even a few feet can...

There is also a common thing called a repeater which is another option but since you have the cable in place, an extender is a better option.

Will vary with the device you install it on. Generally you have to load an app or program to run on your devices and then run the app or program. I suggest you google how to install cyberghost for...

The address may be 192.168.0.1 instead of 192.168.1.1

To get close to your setup, you will need two routers and your modem. Cable to modem, modem to first router, first router attach the PC and the other router (no WIFI), second router is your WIFI...

Go to the TP-Link website and find your router model and country to see what the latest firmware for your router. Note that what is on the website and what is displayed on your device will appear...