how do u train lv5 pokes

if you want to train your ghost pokemons then:
go to NPC fights and fight with bird tamer (he is the last trainer under intermediate trainers).
Have you pokemon moves as blizzard or bolt strike. this 2 moves are strong against his pokemon so you will be able to defeat him easily.

OR

go to NPC fights and fight with swimmer Richards
Use bolt strike on him and it will be easy to defeat him

keep doing either of that and you can easily level up

Hard way:Get toxic and teach it to a pokemon.Get fly and megahorn.And also 40 badges to enter.Lastly go to dark ally and battle the guy.(First use toxic the fly and fly until it is on a low hp then get the lvl 5 poke and kill it(it would take damage from toxic)
Easy way:The one above ^^

how can i get fly and toxic

You get fly by defeating zapmulcuno, the hardest NPC in NPC fights

And you get toxic from buying it at the Dep. Store in the TMs section, which costs $75,000,000 & 4,500 coins.

yea toxic costs a lot but in the end it is worth it, when you have bought it from the dep.store beat zapmulcuno and get fly by defeating it.