Adding an AP One Access Point to an existing LAN

What is the procedure for adding a single AP One Access Point to an existing LAN?

Current LAN has a wireless Linksys or D-Link VPN router and maintained by another IT person (who provided me with admin password).
Wireless router is located in the office and I intend to have the AP One located in the same office (on the wall and not under the computer like the current one).

Range of the current WiFi is very limited and I would like to suggest the replace to Pepwave gear, however I need to take the first step of just showing a big improvement in range by adding the AP One to their network.

What will be the setting on router, I’ll need to modify?
Do you suggest I disable their Antenna for the testing period or they coexist?
Any recommendations?

Thank you,