No need to successively install starting from version 1. Just download and install 3.6.
The 3.6 installer will request the serial number from any previous qualifying version.
Enter your LR2 serial number and the 3.6 install will complete. Same process for the second machine.
Same for LR4. Just load LR4.3 (latest version), enter the LR3 serial and the LR4 install will complete.
