Power second floor of home


My house (previously rented out as two separate apartments) has two main fuse boxes (upstairs and downstairs) the one powering the basement and first floor has power and is good to go, the question i have is how can i power the upstairs box with the downstairs box, the one downstairs is pretty full but im sure i can combine a couple fuses. I'm no electrician but i have good common sense and am pretty handy so any help would be appreciated

Step 1

****This isnt my fuse box they just made me put a picture up***

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