Simply complete Arcade Mode or Extra Mode on any difficulty to unlock the Stage Select feature under Configuration in the Option menu. Toggle the Stage Select setting ON if you want to pick any stage in the game or OFF to play the game normally.
Stage Select (Arcade) - Complete Arcade Mode regardless of difficulty and credits used
Stage Select (Extra) - Complete Extra Mode regardless of difficulty and credits used
Complete Extra Mode once to unlock the 13-Ship Mode setting in Option menu under Configuration. To enable this mode, change your ship stock until you 13. You can also change the order of the ships under a special setting when 13-Ship Mode is enabled. Note that you can only use one credit in 13-Ship Mode.
13-Ship Mode - Complete Extra Mode regardless of difficulty and credits used