As the novella progresses, Gregor Samsa identifies more and more with his body, and less with his mind. He begins to prioritize the basic needs of his insect body (i.e. food, healing from injury, adequate space for crawling). At the same time, he begins to pay less attention to so-called "higher" or "human" priorities: such as his social status, job, and professional aspirations.
Generally speaking, Gregor becomes more accepting of his insect-ness, and less concerned with retrieving his humanity. This shift is demonstrated in a number of ways. He stops asking about his job, for example. When moved to a bigger room, he shows pleasure at having more space to crawl and stretch his insect limbs. Thoughts of his humanity recede into the background of his mind.
Despite this change in priority, Gregor keeps his humanity till the very end. The way that he maintains his humanity is by continuing to care about the people he loves. In particular, he continues to show gentleness, consideration, and concern for his sister. He agonizes over her struggles. The anguish he experinces isn't only from being transformed into a huge bug; it's also from seeing his family and in particular his sister suffer loosing him. In the end, Gregor decided to stop eating, stop moving, and simply die; to relieve his sister from the burdens of caring for him. This act of self-sacrifice is very human indeed.