First up, can you access and the configuration in the router?
Many ISP's don't give their customers access to their routers and keep the login secret or only give absolutley minimalistic configuration options. If you can't acces the required configurations you will have to put in your own router and have it do the NAT (Network address translation).
I will continue as If you had the required acces.
Completly seperating the FTP Server from the rest of the network is probably impossible, but you can inhibit communications between it and other devices in your homenetwork by putting it in a seperate subnet.
Now having a device in a seperate subnet inhibits communication. E.g. the autodiscovery features won't work, but it can still be accessed with the full ip-address.
1.) Seperating the FTP Server in a new subnet.
If you only run the FTP Server on the labtop and want to seperate the whole labtop from the homenetwork that is easy. If that is so continue with 3 else continue with 2
2.) Seperating the FTP Server IP from the laptop IP
To do that I know of two possible aprouces.
1. Set up the server in a virtual machine and configure the host to give it the wanted IP in the network.
2. configure the networkadapter to have TWO seperate IP's and only put the FTP server on one and everything else on the other one.
both abrouces differ with the exact hardware and OS you have installed, so you will have to look them up yourself.
3.) Assingning a new satic IP
Now change it's static IP so that it is in a seperate subnet according to the subnetmask.
That is what that 255.255.255.0 in the network configuration is for. I'm going to assume that your subnetmask is 255.255.255.0 since thatt is the default and if you changed it you probably know what you are doing.
Now look at the IP's of your Homenetwork. They are seperated in 4 "Groups" usually Frist 192, then 168, then 0 or 1 and finally a number between 0 and 255.With the default subnet mask the first three groups determine the subnet.
Now change the IP to something in a different subnet and leave everything else alone ( subnetmask, Gateway, DNS server; ...). Change it to 192.168.10.1 for example.
4.) Change the NAT in the Router
Now you will actually have to access the router. You need to change the NAT, also sometimes called routing tables, so the FTP server remains accessible from the internet.
Find the entries that belong to the ftp server and change the internal IP to the new static IP you just assigned the FTP server. Usually it's entries for port 21, 115, and sometimes several hundred ports for data transfer with really high port numbers.
5.) Test everything to ensure that it everything still works.
6.) Optional:
Look through the configuration options for the router and its manual. you might be able to further seperate the FTP server from the homenetwork by configuring the firewall in the router correctly.