oracle 有具体的操作步骤：
1) Ensure that the release number of your Oracle Standard Edition server software is the same release as your Oracle Enterprise Edition server software.
2) Shut down your database.
3) If your operating system is Windows, then stop all Oracle services, including the OracleServiceSID Oracle service, where SID is the instance name.
4) Back up all database files under the current Oracle home that you must keep.
5) Deinstall the Standard Edition server software. ( It is optional to deinstall the standard Edition software)
NOTE : This step deletes all existing database files that reside under the Oracle home.
6) Install Oracle Enterprise Edition server software using Oracle Universal Installer (OUI).
Select the same Oracle home that was used for the Standard Edition that you uninstalled, or select a new Oracle home. During the installation, be sure to select Enterprise Edition. When prompted, choose Software Only from the Database Configuration screen.
7) If you have an existing database, then point your ORACLE_SID to this pre-existing database.
If your existing database is on Windows, then you must re-create the DB service using ORADIM.
oradim -new -sid oratest -pfile D:/Oracle/app/用户/admin/orcl/pfile/init.ora.1027200811155
8) Start up your database.
NOTE : There is NO need to run the catalog.sql and catproc.sql scripts to convert standard Edition to Enterprise Edition .
Your database is now converted to Oracle Database Enterprise Edition.
You can verify the same from the banner:
SQL> select banner from v$version;
BANNER
-------------------------------------------------------
Oracle Database 12c Enterprise Edition Release
按着步骤升级，还是遇到了问题。
问题一：卸载oracle后，直接安装到原来目录，明明选择了企业版，但是最后select banner from v$version;还是显示是标准版。
重新再次卸载，把注册表中的services/software删除干净，重新启动服务器，把安装的目录也删除了，类似全新安装，安装目录还是和原来一样，新建一个数据库，最后将配置文件、密码文件、控制文件拷贝进去，可以了。
问题二：oracle安装完成后，web应用无法打开了，提示：
System.Data.OracleClient requires Oracle client software version 8.1.7 or greater.
开始以为是client没有安装好，于是有下载一个client 安装，没有用，后来看到有人说是ORACLE_HOME文件夹的全新问题，需要将“Authenticated Users”的权限重新设置，可是刷好后但是还是没有用，重新启动服务器后，OK了。