The best option to install security updates on multiple switches is to use a TFTP (Trivial File Transfer Protocol) server and SSH (Secure Shell) connections. A TFTP server is a simple and lightweight file server that can host the update files and transfer them to the switches over the network. SSH is a secure and encrypted protocol that can be used to remotely access and configure the switches. The technician can use SSH to log into each switch, download the update file from the TFTP server, and apply the update. This method is faster and more efficient than using a terminal emulator and a console cable, which would require physical access to each switch and a serial connection. It is also more cost-effective and less disruptive than replacing the switches with new ones. Using a USB memory stick is also possible, but it would still require physical access to each switch and a USB port, which may not be available on all models.
Reference:
[CompTIA Network+ N10-008 Certification Study Guide], Chapter 5: Network Operations, Section 5.4: Firmware Updates, pp. 283-284
[Professor Messer's CompTIA N10-008 Network+ Course Notes], Section 5.4: Firmware Updates, p. 71
[Professor Messer's CompTIA N10-008 Network+ Training Course], Video 5.4: Firmware Updates, 9:07 minutes