You have two primary options, depending on where you own the game:
Earlier versions (1.143, 1.153, and 1.158) suffered from memory leaks, random desktop crashes during large siege battles, and networking desyncs. Version 1.174 resolved the vast majority of these issues. You can run 500-man battles on mid-range hardware without the infamous "Runtime Error" pop-up. Mount And Blade Warband Version 1-174 Download
The most direct way to get the latest stable build is through the official TaleWorlds download page . You have two primary options, depending on where