new IPS engines are bundled with firmware updates, so upgrading your FortiGate also upgrades your IPS engine.
If for some reason you need a new/updated IPS engine by itself, you can get in touch with Fortinet Technical Support via opening a ticket; they can provide individual engine files if required due to specific bugs, for example.
+++ Divide by Cucumber Error. Please Reinstall Universe and Reboot +++
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