P.s. sorry for my bad English
Fully sync your node first. Unless you are fully synced the CPU will be busy handling the blocks. More connections will come over time. By default the maxiumum is set to 125.
What hardware to you have and how is the node connected to the internet?
I dont think it makes sense to go over 125 connections with 4Mbit/s.
Do you have more than 8 connections? If yes, you just wait and will get more connections once its fully snyced. If not you might have to configure the firewall to allow port 8333.
You can test here -> https://getaddr.bitnodes.io/
if your node is reachable from the outside. You might have to wait till its done with the sync though. It currently shows mine[1] as offline even though its not.
[1] http://213.165.91.169/
For linux you usually can just write bitcoin-cli help
For windows you probably need to give the full path, e.g. "c:\Programm Files\Bitcoin\daemon\bitcoin-cli.exe" help