Upgrade SQL CE Database from 3.1 to 3.5

var engine = new System.Data.SqlServerCe.SqlCeEngine("Data Source=" + filename);

engine.EnsureVersion35(filename);

--HELPER CLASS---

    public static class SqlCeUpgrade

    {

        public static void EnsureVersion35(this SqlCeEngine engine, string filename)

        {

            try

            {

                SQLCEVersion fileversion = DetermineVersion(filename);

                if (fileversion == SQLCEVersion.SQLCE20)

                    throw new ApplicationException("Unable to upgrade from 2.0 to 3.5");

                if (SQLCEVersion.SQLCE35 > fileversion)

                {

                    engine.Upgrade();

                }

            }

            catch (Exception ex)

            {

                Console.WriteLine(ex.Message);

                throw;

            }

        }

        private enum SQLCEVersion

        {

            SQLCE20 = 0,

            SQLCE30 = 1,

            SQLCE35 = 2

        }

        private static SQLCEVersion DetermineVersion(string filename)

        {

            var versionDictionary = new Dictionary<int, SQLCEVersion>

            {

                { 0x73616261, SQLCEVersion.SQLCE20 },

                { 0x002dd714, SQLCEVersion.SQLCE30},

                { 0x00357b9d, SQLCEVersion.SQLCE35}

            };

            int versionLONGWORD = 0;

            try

            {

                using (var fs = new FileStream(filename, FileMode.Open))

                {

                    fs.Seek(16, SeekOrigin.Begin);

                    using (BinaryReader reader = new BinaryReader(fs))

                    {

                        versionLONGWORD = reader.ReadInt32();

                    }

                }

            }

            catch

            {

                throw;

            }

            if (versionDictionary.ContainsKey(versionLONGWORD))

            {

                return versionDictionary[versionLONGWORD];

            }

            else

            {

                throw new ApplicationException("Unable to determine database file version");

            }

        }

    }

Source : http://blogs.msdn.com/b/jimmytr/archive/2010/04/26/upgrade-sql-ce-database-from-3-1-to-3-5.aspx