How to upload an alternative theme..HELP!

There are plenty of free themes on themes.wordpress.net that you can download and then upload into your wp-content/themes folder.

yes! kohaku is telling right thing that there are lots of websites available on net that provides free themes and templates. You can search on Google, you will get many.
Good Luck!

Thank you for the resource but i dont have access to the wp-content/themes folder – my blog is https://safetynut.wordpress.com/ (a free account through wordpress.com) which is a selected template with an edited header.

Could i upload an alternative theme outside of the ones from the selection available.

Read the FAQ over at wordpress.com

https://faq.wordpress.com/category/themes/