I'm no mac expert by any means, but networking fundamentals should be that same.
You will have to setup a point to point (crossover) network.
Basically:
1. Setup a static network configuration on your Apex. Take note of the IP address.
2. Configure a static IP address on your mac using the same settings as the apex, but increment the IP by 1 to avoid conflict.
3. Take an Ethernet cable and directly connect from your mac to the apex bypassing the router all together.
4. Verify point to point connectivity by pinging the apex IP address.
5. Follow the firmware upgrade instructions.
6. Plug your apex back into the wifi adapter/bridge device.
How to setup a static IP on a mac:
http://www.howtogeek.com/howto/22161/how-to-set-up-a-static-ip-in-mac-os-x/
Example of a crossover connection (see example 2):
http://support.apple.com/kb/HT1433
How to ping on a mac:
http://www.wikihow.com/Ping-on-Mac-OS
To avoid all this mess in the future, just get a multi-port bridge for your apex/tank area. This type of wireless bridge has 4+ Ethernet ports instead of 1. You can just plug your laptop into one of the free ports and go. The interface will be auto configured via DHCP just like everything else on your network. The only real requirement for Apex firmware is that both computer and apex are plugged into the same physical device. It does not have to be your router.