How can I improve speed efficiently in OpenWrt?

Good morning,
How can I improve speed in OpenWrt? The case is that I have my internet tester 575 Mbit / s download and 56.7 upload, but in OpenWrt doing speed tests I only have 93.98 Mbit / s download and 49.43 Mbit / s upload.
I have the system mounted as follows:
FritzBox 6591 Cable- This with the original AVM system, here I am allowed to send all the necessary speed to my
FritzBox 4040 with OpenWRT, but still I only have the above mentioned data. Any advice help

Just a random thought (may not be relevant) - make sure you're not using an older cat5 Ethernet cable which would limit your speed to roughly what you're seeing here. I did that before as I was running out of cables in the house and it took me a while to figure it out.

cables are all cat6, and i have already tried changing the cable.

Cat5 cabling can handle speeds up to 1gbit. The real issue presents itself whether it's stranded or solid. You want solid because of the better construction and it goes a longer distance. Most manufacturers use stranded for patch cables which lowers the price significantly but also lowers the quality of the connection. Cat6e (commonly) adds higher MHz and a little longer distance. The main benefits being more twists, a pvc partition, and a thicker jacker to prevent crosstalk/interference.

cat6 plenum utp (unshielded twisted pair) is the right choice for most every situation concerning </= 1gbit.