I want to change my derailleur from a Tourney TY-300 to an Altus M2000. What bike parts do I need to change? I want to change my derailleur because i mostly ride forest trails and I have heard the new m2000,3000,4000 are for mtb bike.i have a big buck bike And I wanted to upgrade the derailleur because my derailleur got bent a little bit because of an accident and after sometime it got more bent because of me riding trails so that why I want to change it and because the derailleur doesn’t shift good and the bike mechanic shop near me said there is no fix for this derailleur and that he Could only adjust it and that fix would only be temporary.so I have to choose between getting a new ty-300 derailleur or upgrading to an actual mtb derailleur
Assuming you want to upgrade from a Tourney 7 speed group component to an Altus M2000 is 9 speed.
You'd obviously have to change the rear derailleur, shifters, rear sprocket cluster and chain. Presumably you have 3 chainring crank, Altus M2000 comes in a 3x9 option. You'd have to swap the front derailleur but you might be able to keep the crankset.
However, you need to look at your rear wheel. If you have an old style freewheel (sprockets and pawls mechanism in a single unit) you can't upgrade it to 9 speed. If you have a freehub and sprocket cassette (ratchet mechanism is part of the hub), you may be able to upgrade to 9 speeds. The freehub body for 7 speeds and below is narrower than those for 8 and above. If you have a 7 speed freehub, you can't upgrade to 9 speeds. If you happen to have an 8+ freehub with a 7 speed cassette and spacer you will be able to. If your rear wheel isn't compatible, you'd need a new one that is.
If you have to swap out the whole drivetrain, crank and rear wheel it's probably just not worth doing the upgrade, especially when you factori in the cost of having a bike repair shop do it for you, or the cost of special tools you'd need to do it yourself.
Shimano derailleurs thru 9 speed will work correctly with any Shimano 7, 8, 9 speed shifter and, therefore, the RD-M2000 would work in this situation.
Based on your situation of damage to your rear derailleur, you must be sure your derailleur hanger--the piece where your derailleur attaches to the bike frame-- is in proper alignment. Not bent or damaged. I'll defer to your bike shop guy, as that is one aspect of derailleur "adjustment" and perhaps what he is referring to.
Again, based on your brief sketch of your riding style, perhaps upgrading to a newer mountain bike would be a good investment. As Argenti's answer, describes, there's quite a bit of componentry to switch out if you'd like more of an upgrade with increased speeds. I'm not sure what a "big buck bike" is, but your local bike shop should let you test ride their selection. A quality, entry-level mountain bike will come stock with M2000-3000-4000 components at a very reasonable price. You'll gain wider-range of gearing, modern geometry of the frame, brake options that include disc brakes, and a variety of suspension options.