Use Properties|EOL-Style to change the EOL-Style (line separator) of the selected files. The EOL-style is used when updating or checking out a text file and results in a corresponding conversion of its line endings:
In the project settings, the default EOL-style which will be applied to every added file can be specified. By default, this will be Platform-dependent.
When changing the EOL-style of a file, SmartSVN checks whether the file has consistent line endings. If this is not the case, it will reject to change the EOL-style (other behaviors can be configured in the project settings). To skip this check, use Force.