Presuming you mean the centerfire Model 55 lever-action, and not the rimfire Model 55 auto-ejecting single-shot:
After double-checking that both bbl & magazine are empty, lift the takedown lever located at the front end of the magazine tube & unscrew the mag tube about 1".
Open the finger lever, then turn the barrel about 1/4 turn to the left.
Draw the bbl, etc, forward off/out of the frame/receiver.
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