Direct this kind of question
here.
As Kondou said above, if you just press the Upload button again, it will update your beatmap listing to have the newest version of your map. However, if you upload your map, change it, and then update to the latest version, it will discard all your local changes, so be careful!
Check out
ShareX if you want to share your beatmaps without uploading.
Simply install ShareX or
puush, go to your beatmap in the editor, and "Export Beatmap Package" - this will create a .osz which you can then upload with ShareX or puush and link to friends.