you should read this http://ez.no/doc/ez_publish/upgrading/upgrading_to_4_0/from_3_10_x_to_4_0_y
I've done this many times successfully. Note that If you are in cluster mode, you'll have to uncluster your binaries doing the migration.
Hope this helps.
Arnaud
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yes, do read this documentation.
You will probably have to upgrade from 3.10.0 to 3.10.1 on your local servers and the upload the data (SQL dump etc) to your hoster's webspace. Depending on your custom design in 3.10, you will need to do some design fixed, of your design is based on the ezwebin design. The reason for that is, that ez 4.01 uses ezwebin 1.3, while ez 3 uses ezwebin 1.2 .... The HTML that is created is _slighty_ different.