Hi Per,
First you are going to need to install a VNC server and a FTP server on the remote computer and have them run at startup. You will then need a VNC client and an FTP client on your computer.
VNC server/client as well as a FTP server are available on hobbes for an FTP client I use jFTP.
Once those programs are setup and running all you need to know is the IP address of the remote (I think you can set that to a fixed IP via the RT-AC1750 but you need to check that in the manual).
Depending on how you connect to the RT-AC1750 you may need to set a pass through to the remote computer. If you are connecting via a WAN IP address you should have a VPN box at each end for security, if on the other hand you are linked via the RT-AC1750 wireless there should not be any problems.