I created a map with the size of biomes 3, but I wanted to change to 4, because the biomes are very small. Is it possible to change without using external programs? I have seen a changing youtuber, I do not know if I was editing some file of the game by notepad, or a command within the game. Help me.
The only way to change it without external tools is to recreate the world and change the biome size in the Customized settings, then copy the level.dat file from that world to your world. replacing it. Note that you must store your inventory, including Ender chest, in a chest or they will be lost because this will reset player data; it will also reset some data associated with the End and the time (this has an effect on regional difficulty), and if you are using mods, their data can be affected as well.
However, I'd suggest downloading NBTExplorer and editing the "generatorOptions" to change "biomeSize" from 3 to 4 to avoid possible issues with just replacing a file (either way, make sure you backup the world before you make any changes to it).