On WikiTree one does not upload DNA, rather one links his or her account. You simply need to input information about the DNA tests which you have taken. You can access the input here:
Select on the drop-down menu which test you took (e.g. 23andMe, Ancestry DNA, Family Tree DNA, MyHeritage etc...), or which database it is in if you've uploaded elsewhere. Then include comments, if desired (username, haplogroup?), to help others connect with you. That's it.
To get the most out of your DNA connection here, it will help for you to add your family tree. To do that, you'll first need to sign the Honor Code and get confirmed as a member by "volunteering" -- essentially stating that you're keen to participate, working with others, to contribute to the global family tree. The shape and extent of your contributions is up to you, but it ensures that everyone is on the same page:
Also don't worry too much about the comments explaining your interest. If you're new to genealogy, for example, you can just say that. It's good to say that you're interested in collaborating with other genealogists, since that's what WikiTree is all about.
Once you're set up, and you start adding ancestors and biological relatives on WikiTree, your DNA test will be linked on the profiles of your ancestors, indicating to others that you have taken a test, essentially giving them a heads-up that you're willing and able to share and compare results.
After that, you can enter into the world of "DNA confirmation", i.e. sharing the genetic evidence of your genealogical conclusions.
I hope that overview helps explain the DNA side of things here. Remember that there are also official help pages explaining things on WikiTree, but if you can't find an answer there, ask a mentor, greeter, or here on G2G.
Best of luck!