Wanting to improved Pokémon stats

[Pata733]

I have a Gallade that has pretty good stats, but I want to know if there a way to improve his stats. Please let me know.

[Ven Enfield]

To improve a stat of pokemon well there's just some ways
IV - these are Initial Value you get this as soon as you get the pokemon the maximum is 31 per stat and that is fixed you can't change this one that Pokemon will have that for the rest of your gameplay
EV - these are Effort Values these are trainable you can use vitamins to speed up the process but there's a limit of 100 EV for vitamins so once your pokemon reach 100 EV the only way to improve it is to fight pokemons, each pokemon you battle give a different stat like Noibat give 1 Speed EV you can search online about EV yields of each Pokemon so you can see where you can train or what Pokemon you should fight, the max EV per 1 stat is 255 (correct me if I'm wrong) but I usually keep it 252 since usually 6 EV points = 1 stat points and the max for overall EV you can train is 510 so let's say you train two stats, Atk and Speed so I got 252 for each of em and 6 EV to whatever I think would be good to increase just a bit, it's really up to you how you train your pokemon really.
Nature- it improves your stat even more usually with a cost of something that would go down, for example Modest nature gives SP atk + and - Atk stat , if I remember in reborn you can change the nature of your pokemon in 7th Street where he needs Heart Scale for it but I think it's randomised again I'm not sure

Here's my Garchomp stats to be an example for you 
Its nature is Jolly ( +Speed, - Sp Atk)
 

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[Pata733]

I know I can't change ivs, I meant a mod that can change his initial value. If there is one.

[Waynolt]

The official way would be to chain breed them.
Else, you can either cheat (with the Debug mod from Aironfaar's Mod Box or with the Sandbox) or use EvOverflow (from SWM - slower than breeding, it's mostly for roleplay purposes)