Need Help..

[Niwashi]

To turn your level 50 Marauder into a Warrior, you'll need to get a few quests further in the Main Scenario quests (up through level 20 Slyph Management) if you haven't yet, and get Gladiator up to level 15. Then you can do your Warrior quests (all of them, since you're already at level 50). You'll also want to continue Gladiator up to level 34 and Pugilist up to 42 at some point for Warrior's cross class abilities. (The GLD level 22 one, Provoke, is especially helpful.)

To then unlock endgame content, you have to complete the Main Scenario quests. Since it sounds like you're way behind on this, it will be your main focus for quite a while. I'd suggest combining this with leveling up your GLD and PUG for cross class abilities. Level one or both of those to whatever level you left off at on the Main Scenario, and then use those classes to do the remainder of your Main Scenario Quests. This way the quest XP can go towards leveling them. (Or at least use them until they reach the level 34 and 42 goals you want for your cross-class skills. For the last few levels worth of quests, you could go back to your Warrior if you prefer.)

As it seems you have a lot of catching up to do, I wouldn't worry about your MRD/WAR gear for right now. You'll be doing a lot of lower level quests until you catch up in the Main Scenario, so you mainly need gear that matches (or slightly exceeds) the level of questing that you're at. Pugilist will need separate leveling gear than what you used as MRD, but that's about it. If you do want to upgrade your MRD/WAR gear anyway, you can either purchase stuff from the Market Board or you could try hunts to earn Tomestones and Allied Seals that can be traded for some nice endgame gear once you accumulate enough of them. (There will be other ways to earn tomes later, but I believe hunts are the only way that's not locked behind finishing the Main Scenario first.)