What parts do I have to change if I want to change my derailleur to higher speed? 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.