The meanings of Jacob's old and new names may give us a clue as to why his name was changed. "Jacob" means "heel catcher" or "supplanter". It implies getting the better of someone else by devious means.
In Jacob's early life we can see this trait in him when he had tricked his brother Esau who complained:
36 He said, “Isn’t he rightly named Jacob? For he has supplanted me these two times. He took away my birthright. See, now he has taken away my blessing.” He said, “Haven’t you reserved a blessing for me?”
Jacob's name was initially changed when he wrestled with a man who, we later learn, was an angel. Jacob became lame teaching him to trust in God, not in his own cunning:
24 Jacob was left alone, and wrestled with a man there until the breaking of the day. 25 When he saw that he didn’t prevail against him, the man touched the hollow of his thigh, and the hollow of Jacob’s thigh was strained as he wrestled. 26 The man said, “Let me go, for the day breaks.”
Jacob said, “I won’t let you go unless you bless me.”
27 He said to him, “What is your name?”
He said, “Jacob”.
28 He said, “Your name will no longer be called Jacob, but Israel; for you have fought with God and with men, and have prevailed.”
31 The sun rose on him as he passed over Peniel, and he limped because of his thigh.
Commentators vary on what "Israel" means, but they all have the idea of "overcoming with God".
This contrasts with the meaning of the name Jacob. God later reminds Jacob of his change of name and of promised blessings:
9 God appeared to Jacob again, when he came from Paddan Aram, and blessed him. 10 God said to him, “Your name is Jacob. Your name shall not be Jacob any more, but your name will be Israel.” He named him Israel. 11 God said to him, “I am God Almighty. Be fruitful and multiply. A nation and a company of nations will be from you, and kings will come out of your body. 12 The land which I gave to Abraham and Isaac, I will give it to you, and to your offspring after you I will give the land.”