To be fixed in one's ways means to be unwilling to change something that one has always been doing.
1. When the soccer team lost five consecutive games in the English Premier League, the officials decided to sack the coach as he was fixed in his ways of training and did not adapt to the game situation.
2. Harish' business partners were adamant in not changing the product's colour as they were fixed in their ways.
3. The webmaster refused to change the site template even though it looked tacky as he was fixed in his ways.