To install an FTP server, try out vsftpd. To install, just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:

sudo apt-get install vsftpd

Once installed, you need to edit the config file

sudo gedit /etc/vsftpd.conf

Make sure that you change the items shown in the image below.

Once done, do

sudo service vsftpd restart

For more info and documentation, visit vsftpd and FTP Server Guide on Ubuntu