For starters, download the latest version of the free Uniden Sentinel software from here (download link at top of page):
Then when the scanner arrives, update database and firmware by following directions on page 16 of the owner's manual. You can download the software now before your scanner arrives and look it over.
Sentinel is required for database and firmware updates, but for a much more feature rich software, I would highly recommend having a look at ProScan:
Computer Aided Scanning Software for the Uniden BC125AT BC250D BC296D BC346XT BC346XTC BC780XLT BC785D BC796D BCD160DN BCD260DN BCD325P2 BCD396T BCD396XT BCD436HP BCD536HP BCD996P2 BCD996T BCD996XT BCT15 BCT15X BR330T SDS100 SDS100E SDS200 SDS200E UBC125XLT UBC126AT UBCD3600XLT UBCD436PT...
proscan.org