It’s quite simple to change ascended armor and weapon stats in Guild Wars 2 (GW2). In order to do so, you will need the following items:

1.  The base item to change
2.  5 Globs of Ectoplasm
3.  Anthology of Heroes (can be bought in the mystic forge vendor Miyani in Lion’s Arch for 10 Spirit Shards)
4.  The Exotic Insignia for the desired stats. Example: Marauder Intricate Gossamer Insignia
5. Add all the items to the mystic forge in Lion’s Arch and voilà!

You can check a list of stats combinations in https://wiki.guildwars2.com/wiki/Attribute_combinations, then craft or buy the insignia for the desired stats.