Extract cab content using any software like winrar/7-zip or whatever.
Obtained content copy to your navi SD card, in to the root of the LoquendoTTS folder.

Problems that sometimes occur are related only if you had an older edition of the engine (Loquendo 6). In that case,
first - bekap
then - delete the old "data" folder (LoquendoTTS\Data)
and old "bin" folder (LoquendoTTS\bin)
keep LoqAudioBoard.so and "LTTS7AudioBoard.so if you can not find them.

Then you need newer files as well: LTTS7AudioBoard.so and LoqAudioBoard.so, which you place in LoquendoTTS\bin\
Usually present in newer navcore's.