For advance user = edit version of Angel Online in "reg.ini"
For complete guide, please follow this step:
You may see many files in there. That Angel Online game files
2- Select "reg.ini" and open with our notepad or other word processing
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3- After you opened "reg.ini", you can see your Angel Online game version there.
Mine(at this time) is version 2.5.1.3. You can see picture below for detail.
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4- Just change the current version. For example, make it older version. At this time, I set it to version 2.5.1.2
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5- After change the current version to older/previous version, make sure you save it. You also can save by pressing CTRL + S
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6- Last step is, run "start.exe" again then you will see game launcher try to re-update the files.
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Hope this guide is useful and also works for you :)