I am creating my own theme but I frequently make changes. When I try to upload a new version of the theme it sometimes ignores the changes or I sometimes get two themes or on the file system the theme directory has two themes.

I can't pin down when and where it doesn't work but uploading a new zip for me doesn't work. The changes are not applied.

The only way I've been able to get it to work is:

1. Activate another theme (deactivating my theme)
2. Delete my theme
3. Upload the new version of my theme
4. Activate my theme

Is it possible with WordPress to simply update my theme with one step, without deactivating it?

1. Upload new theme and it's applied