The Rangers have gone through many roster, Zord, and power changes. Rita gave the Dragon Coin to a new student at Angel Grove High - Tommy, who fought against the Rangers as the evil Green Ranger, and later joined the team once the spell over him was broken. Tommy eventually lost his powers as the Green Ranger and gained new powers as the White Ranger.
To defeat Lord Zedd, who arrived to take over Rita's task, the Rangers needed to upgrade their Dinozords into Thunderzords, and later bring back Tommy as the White Ranger. Shortly after, Jason, Zack and Trini left for Switzerland to attend a peace conference, and left their powers to three allies of the Rangers - Rocky, Adam and Aisha, who became the new Red, Yellow, and Black Rangers.
When the team lost their powers after an attack by Rita's brother Rito, the Rangers took a trip to the Temple of Power, where Ninjor gave them new powers and Ninja Zords, which were later joined by the Shogun Zords.
Kimberly's departure to train for the Pan Global Games paved the way for Katherine, who took her place as the Pink Ranger. The Rangers' Power Coins were stolen by Goldar, and destroyed by Rita and Zedd, putting an end to the Power Rangers as we knew them, and setting forth the events that would transform them into Zeo Rangers.