VP-BC73 Square Taper Sealed Bearing Bottom Bracket

How do I tell which size without removing my existing bottom bracket?

First option would be to pull the crank arms, then measure the spindle length.  

Second option would be to look for the model of your crank, and see what bottom bracket spindle length is recommended for that crank.  

The third option would be to see if the manufacture of your bike listed the stock bottom bracket dimensions. 

Each option would,  of course,  require you to measure or know your frame’s bottom bracket shell width.  This is easy to do without removing the crank. 

Reality is, published data can be wrong or not correct for your set up.  Measuring is always the best way to know for sure.