This information is from TortoiseSVN Help
To undo all changes you made in a file since the last update:
- Right-click the file to access the context menu
- Select TortoiseSVN -> Revert A
- A dialogue box will appear showing the files have been changed and can be reverted
- Select those you want to revert and click on OK
Revert will only undo your local changes.
It does not undo any changes which have already been committed.
If you want to undo all the changes which were committed in a particular revision, refer to Section 5.8, "Revision Log Dialog" of the TortoiseSVN Help