chivick258 Emir-says You will need a pc if you want to mod an apk file.
Then you can download softwares like "Apk Tool" or "Apk Edit" to mod the file.

To upload an apk file, you need to have the raw file, that is if you want to upload a Pes 2014 game, then you should have a file like Pes 2014.apk