As far as I know Web Usage Controls were released in AsyncOS 6.3 for Web

I've not seen an specific migration guide other than what is in the user manual which you can get off the Ironport portal site.

There isn't a 100% direct match between the categories that are in URL filters and WUC so it's not easy to create a automatic process for mapping.

Remember when you switch between URL Filters and WUC it wipes all the Allow / Deny settings in the access policy  which have been set against the pre-defined categories. (Your custom categories remain unchanged)

So migration strategy would be something like.

Upgrade to 6.3

Backup Config (and label as 6.3 with URL filters)

Switch to WUC

Redo allow / denies for all the categories (or if you have an M-Series you can push it across)

Backup Config (and label as 6.3 with WUC)

Now you have 2 configs you can use for switching between WUC and URL Filters.