@monikakm
The link speed is the data transfer rate between WiFi connected devices and the WiFi router (hot spot) itself. As B. Diddy points out, this is not the same as your internet speed. However, if you have a really slow internet connection, having a fast WiFi router can help when devices on your WiFi network talk to each other (like sending data to a printer, for example).
Switching to a different band on the WiFi router can result in problems if, for example, you have other devices in your area (your home or perhaps your neighbor's home) which use the same band and interfere with your use (or you interfere with their use). I've seen interference from devices such as wireless phone handsets, wireless audio repeaters, etc. Also, it does no good to switch to the 5GHz band if your WiFi device doesn't use this band.
The bottom line is that if you switch to the 5GHz band and are happy with the performance you get, you should stick with it. However, there may be other considerations. You can do a Google search on the differences between 2.4GHz and 5GHz WiFi router bands and see what you get.
Good luck.