You already have it, the D|S program installer includes the basic dynamics plugin. If you have the latest program version, you have the latest plugin version.
Your actual problem might be the same as what I think I’m getting now that I’m making more effort to get used to 4.5 — some items, in particular some dynamic clothes, either didn’t save their /data/ files properly in D|S3, or D|S 4.5 is misreading the data folder location from the old scene files. I think I’ll have to file a support ticket for this, it’s a bit of a head-scratcher.