You can use the migration tool http://sitefinitymigration.codeplex.com/ to migrate the data from 3.x to 4.0. The tool uses web services and it does not operate with the database directly. You need to patch your project to Sitefinity 3.7 Sp3+ / or 3.7 Sp4 /. Also make sure to backup your files first. Here are the official upgrade instructionshttp://www.sitefinity.com/support/upgrade-instructions.aspx
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You can download a trial of Sitefinity here.
The current version of Sitefinity is 5.4, so you can log into your Sitefinity.com account and choose to activate the Standard Edition trial -