Welcome to BlackBerry Forums. Take a deep breath and we'll get through this
You need two pieces of software - Desktop Manager, which is available from the RIM BlackBerry Web site, and the actual Handheld Operating System for the 7250. A good place to start looking is here - BlackBerry Operating System Downloads - BlackBerryFAQ
You can go directly to the Verizon download website at BlackBerryÂ® Software Updates
Let's assume you have Desktop Manager installed.
Download the 7250 handheld OS from the Verizon web site
Install it onto your PC
Restart Desktop Manager - if Application Loader does not automatically kick in, click on it
The OS should now be loaded to the 7250.