I'd like to upload my 2015 tax return into turbo tax. How can I do that? If i need to upgrade my account, I am happy to do that. I just need to know the steps so I can

I assume that you are talking about a 2015 tax return that was not prepared with TurboTax Online. Is that correct?
What do you mean by "upload"? Are you just trying to store a copy of the 2015 tax return in TurboTax Online, or do you want to transfer information from your 2015 tax return into your 2016 tax return in TurboTax Online?
Do you have a PDF of the 2015 tax return that you want to upload?
If you want to transfer information, what software did you use to prepare the 2015 tax return? If you used the CD/Download TurboTax software, do you have the .tax2015 file for the return?

I used turbotax, the downloaded application. But now I want to be able to import my results from 2015 online so that I have easy access to the data the same way I can see everything for 2016. Is that possible?

Yes, I do have the .tax2015 file!

It's still not clear what you want to do.   Are you currently preparing a 2016 online return and want the 2015 data to transfer into the return so that you don't have to fill out information such as name, address, dependent info, etc.?   Or are you asking how to add your 2015 desktop return to the 2015 Tax Timeline merely so it will be in the same place as your 2016 return?

I just want it in the timeline. so i can access it in the future

It is best to keep the PDF & tax files on your computer for safe keeping since online access requires that you continue to use the Online program every year ...  

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that'll do. thanks!

You can't add a desktop return to the Tax Timeline.

It is possible to add a file to the section called "MY DOCS", which is an online storage area.  I'm not sure I would do that, however.    You may have to keep using  a paid edition of Online TurboTax each year to maintain access to MY DOCS.  So as far as I know, if you don't continue paying each year, you could lose access to any documents you add.

https://ttlc.intuit.com/questions/1898861-what-is-my-docs

https://ttlc.intuit.com/questions/2263274-how-do-i-upload-documents-to-my-docs

If you archive the file yourself on your computer and/or any external storage media, then you have complete control over it.   I usually archive the tax data file *.taxYYYY, and 2 PDFs--one PDF of the return "as filed", and one with "all forms and worksheets."

NOTE:  Remember all PDF tax documents and data files are very sensitive files, since they contain your personal ID info, financial data, and possibly bank account numbers, etc.  Be sure to store them safely and securely to guard against computer theft, hacking, etc.