I am a returning player to game, after a 2 year hiatus, and I am trying to deiced if I need to change my advance class from jugg to marauder. I have read an old post that advises me to do so , because I prefer a Dps build instead of a tank build., but at the same time I don't want to start completely over. (meaning I don't want to lose what I have accomplish in game.) I don't mind learning how a new advance class works. i just don't want to grind my way to end game content again. If this is possible would someone please chime in and mention how this is done. I would really appreciate it.

Also were could I find a good DPS build for a Sith Warrior. I tried Dulfy but couldn't find one for the Sith Warrior.

You cannot change your advanced class. If you have a Jugg, then it will always be a Jugg. You would have to make a new character if you want to try Marauder. The good news is that leveling is actually quite fast now. There is also a 250% XP event going on right now, up until patch 5.2 hits (sometime early April is the current ETA).

Marauder is a good class overall. Carnage and Annihilation specs are solid in endgame PvE. All three specs (including Fury) are good in PvP as well.

If you really don't want to tank, then yeah you might want to switch. Vengeance is a fun dps spec, which has mediocre performance in endgame PvE and mediocre to poor performance in PvP.

Here is a great resource for optimal PvE stats, for endgame PvE gearing: http://www.swtor.com/community/showthread.php?t=847112

Here is a link to the Dulfy 5.0 class guides: http://dulfy.net/2016/12/22/swtor-5-0-class-guides-master-list/

If you were searching the Dulfy site for a "Sith Warrior" guide, you would not find any. Warrior is the generic term for both Mara and Jugg. Nowadays, you have to pick either Mara or Jugg at the character creation screen. So you start at level 1 as either a Jugg or Mara, which is different from how it was done in the past (chose advanced class after level 10).