LSM (Ziess LSM microscope image) files seems to be based on TIFF graphics format, so there is always the possibility that your .lsm files are just that, renamed .tif files. The easiest thing you can do is to check whenever renaming the suffix from lsm to tiff works, if it does no lsm to tiff conversion is required.
Unfortunately, we weren't able to find a software that could be otherwise used to convert or export lsm to tiff.