@LetitiaB 

Hey

The only setting you could adjust would be the Radio Power, set it to FULL instead of AUTO.

I have to be honest and say that range on WiFi is very subjective, never believe the stats as they are the theoretical maximums.  Its a bit like MPG for your car, its never what the manufacturer claims in the real world.

Yes you are correct that they claim 300m range for WiFi, but from years of experience that aint ever going to happen.  Few reasons for this

1.  Thats in a PERFECT scenario with no obstructions, interference or anything

2.  Its also 300 from edge to edge, not AP to edge.     Basically if you have Phone1 150m to the right, AP in middle and Phone2 150m to the left, you have 300m of range.. its really not, but kinda is also as you could walk that 300m without disconnecting..  This AP is designed for Middle (omnidirectional) range.  

3. Its an omnidirectional antenna, its designed to blast evenly in all directions, where you want it focused in one direction (directional or sector antenna)

OK to fix this, few things..

Try MAX power, may help... may not

60m is not unachievable, but from experience its fair distance for Omni-Directional.  If you have an android phone try WiFi Analyser app, look at the signal strength.  This will be rated in -db (loss in decibels).   In short you will always lose something so this is never 0, range is likely -40 to -75.   At -40 its near perfect signal, at -55/60 its good.   At -75 its mostly noise now, will be slow and after that you are dead air.   Look to see what you are getting at 60m and update us

Is there another AP in your area?   again WiFi Analyser will tell you this, if so change channel to avoid interference.  

2.4ghz will travel further than 5ghz, but will also be slower. 

You could invest in a Directional antenna.   That focus the beam in the direction you want, rather than all over the place

Lastly.   Buy a second AP and use MESH to repeat the signal.  This has worked for others, however that adds costs (if that is an issue).