cannot access shared network drives

OK dumb user here.... I'm not sure if this is the correct location to post this question but here goes. This past Friday I had Fiber Internet installed in my home, I'm using my Netgear Nighthawk R7000 AC1900 to provide the wireless in my home (1800 Sq feet). My desktop is hardwired directly to the ATT modem as well as my Nighthawk. My wife's laptop uses a wireless connection. Currently, both PC (Windows 10 x64) can access the internet but my wife's laptop can no longer access the shared devices (hard drives, printers) on my desktop. After the tech installed the modem he mentioned that the IP address is 192.168.1.254 this has created a lot of issues for me. With my previous ISP the modem IP was 192.168.0.1 and everything worked as expected.

I can login into the ATT modem and I see where I can change the IP address if I change the IP address what other changes do I need to make?

Do I have to call ATT and let them know I have changed the IP address?

Anything else?

My assumption is that if I change the modem IP address to the previous address all of my connections issues will be resolved. If this is not a correct asumption please let me know and what action I should take. Also please remember to provide instructions for dummies. 

For the IPCONFIG command, the following is what I see for my desktop

Following is what I see for my wife's PC