Thank you very much for your answer!
Unfortunately, I didn't manage to solve the problem, following your instruction.
I created the table with KEGG protein names in the first column and normal IDs in the second one, While uploading, I'm choosing KEGG names as the key col. Nevertheless, Cytoscape creates another column in the node table, but it's absolutely empty! I tried string and integer values as the ID and none of them were recognized succesfully, What can be a reason of that?
P.S. Sorry for possible mistakes, because English is not my native language and I'm still learning it.
N.