i don't see any improvement on my internetspeed
Nothing is wrong. No router from any manufacturer can take the Internet speed that it receives from the Internet Service Provider (ISP) and make it go faster. If you need faster Internet speeds, you will need to talk to your ISP about a faster Internet connection plan.
and wifi range.
The WiFi broadcast power of routers is limited by law. Just about every manufacturer is running their routers at the max, so......despite what all the fancy advertising might imply.......you should expect wireless range to be about the same from router to router from different manufacturers.
The possible exception might be a router that has large external or "rabbit ears" type antennas, which would broadcast the signal a bit more efficiently.