Check the Release Notes of the higher version you hope to upgrade to, and it will have a section Upgrading to This Version, with a list of previous releases, that can upgrade to that version.
I remember writing a KBA-1845: Recommended firmware and Suggested upgrade path for Zonedirector, and we list those you can skip/upgrade past. Here's your blurb:
ZD Model : ZD1100
Upgrade Path:
9.1.2.0.8 >> 9.3.4.0.15 >> 9.4.3.0.22 >> 9.5.3.0.44 >> 9.6.2.0.13 >> 9.8.2.0.15 >> 9.9.0.0.212 >> 9.10.0.0.218 >> 9.10.2.0.73 (9.10 MR2 Refresh5 for ZD1100)
NOTE: Not all APs supported in early versions, are supported in later releases. Check the intended version Release Notes for Supported Platforms -> Access Points, to be sure your ZD1100 still can manage your current model of APs.