Using open source code in my final year project I am a final year undergraduate student reading for Bsc. Electrical and information Engineering. As for the final year project, I am planning to do a project on deep learning. After doing some literature survey I found a research paper that goes along with my research interest, and the project code is also available in GitHub.I want to recreate the research paper and do some additional changes to their research methodology and evaluate the results.I just want to know if it is a plagiarism to use that code, and will there be any obligations, if I am to write a research paper using my experimental results including the additional changes to the research. 

Thanks in advance and sorry If am being naive, as I am new to this domain. If some one could be of any help to clarify this, it would be of great help.
It is not plagiarism as long as you clearly write something to the effect of "I downloaded this code from this github" in your paper and cite the paper in question. Plagiarism would be to pretend that you wrote all the code from scratch.

(On a side note, the code on github is most likely under an open source license, but you should double-check this before you upload your modified code to github. If there is no license present in the project that explicitly allows it, it would theoretically be a copyright violation to publish your modified code. This doesn't affect the paper, which you can publish even if you can't make your code public.)