Problem with internal memory Sony Z3

Hello, my Z3 seems to have the internal memory almost full, the file manager tells me that more than 90% of the available space is occupied. Actually, looking at the details of the file manager, it tells me that over 10 Gb are classified as "Other", that means no music, photos, movies, etc ... If I open this category "Other" the file manager says it has a total dimension of 1.13 Gb (instead of 10 as indicated at the upper level) and that in this category the larger folder is the Android folder (842 Mb), while all the other folders occupy just few space. All media files are stored in the sd. I wonder where is hidden all the "stuff" that has virtually saturated my memory. I'd like to delete this stuff if it is possible. Can you help me please?
Thanks so much

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