Are you looking to update to 3.74 to access the PlayStation Store, or are you hoping to modify your Vita with homebrew? Let me know, and I can provide specific instructions for either path. PS Vita System Software (US)
New mass-produced SD2Vita adapters (which let you use microSD cards instead of overpriced Sony memory cards) often ship with instructions that say "Requires FW 3.74 Hotfix." The adapters work on older firmware, but the installation wizards have been updated to check for spoofed 3.74 to avoid user errors. ps vita system software update 374 hot