how i can migrate back up sambapos2 to sambapos 4?
Backup your database for safe-keeping in case anything goes wrong.
Without doing a full migration test, I make no claim to how easy or difficult this is, nor how successful.
The upgrade path should be:
2.99c 3.0.35 4.1.82
Be aware that V4 requires .Net Framework 4.5 assemblies which are only available in Windows 7 or higher. Windows XP does not have support for .Net 4.5 , therefore you cannot install SambaPOS V4 on an XP machine.
If you are using SQL CE (Compact Edition), it is highly recommended that you upgrade to SQL Express 2014.
Other good information: