how do i download freescan to program a uniden bcd996p2
You don't indicate your location. But, if you have any DMR (also known as MotoTRBO) or NXDN systems in your area (and you have purchased the update from Uniden for one, or both, of those system types), FreeSCAN does not support DMR systems correctly, and has zero support for programming NXDN systems.
Ronaldski has given you the link to the user guide, which is an excellent place to start. However, if you have DMR or NXDN systems to deal with, or want additional options for logging, importing systems, and controlling your scanner via PC (FreeSCAN allows controlling, but ProScan has more & better features), then consider trying
ProScan. You can download & install ProScan for a thirty day free trial, before you'd have to either quit using ot, or purchase a license to continue using it. The one time cost is $50, and any updates released are provided at no additional charge. ProScan also supports multiple Uniden scanner models, from your P2 scanner, to the x36HP & SDS series, as well as a large number of other scanners, including some that were discontinued decades ago.