Mac

On a Mac, you can easily use the Automator app to easily replace incorrect characters. Ensure you have a backup of all your files just in case.

1. Open the Automator app (should be preinstalled)
2. New > Workflow 
3. In the Variables search field, enter Get Specified Finder Items and drag that action to the right
4. In the Variables search field, enter Rename Finder Items: Replace Text and drag the action to the right (if prompted to make a copy of the file, do not add the copy since you should already have a backup of all your files)
5. To replace spaces with underscores: 
   1. Select Replace Text from the drop down
   2. Enter a space in the Find field
   3. Select basename only
   4. Enter an underscore _ in the Replace field
      
6. To remove parenthesis
   1. Select Replace Text from the drop down
   2. Enter ( in the Find field
   3. Select basename only
   4. Keep the Replace field empty
   5. Drag another instance of the Rename Finder Items: Replace Text to the right
   6. Select Replace Text from the drop down
   7. Enter ) in the Find field
   8. Select basename only
   9. Keep the Replace field empty
7. When you are ready, test with one sample file first and drag it into the Get Specified Finder Items 
8. Click the Run button on the top right
9. Check the folder with the original file (ensure you are not looking at your backup folder - your backup folder should remain untouched)
   
   

Windows

Search on Google for "batch update file names" to find a variety of simple to use tools.