TRAIN
You have to be doing the quest: A soul's bane to hit the hit of 200 (Members Only.) Otherwise is would be around 60-90 with a armadyl godsword (Sources from Old answer) requiring 99 str, 99 att and 99 def (99hp would be recommended)
There is a girl that has 99 on all skills her runescape name is 'xxphatmagexx'.
The total exp is 13,034,431 experience for a 99 stat on RuneScape.
you train it
There are no cheats in RUneScape. Getting level 99 in ANYTHING requires a considerable effort.
you keep training your skill to get up to lvl 99
I guess you could do bandits!:D
Fish Salmon & Trout in shilo village to 99.
By fighting.
Spend time on a stat and train it for experience. Once you get enough, you can be 99.
It depends how long you are on Runescape.
level 138. there is no higher level on runescape (for players)