If you use any of the auto install options, you may lose something as it automatically shrinks some partition to make room for the new install.

But if you use Something Else or manual install you will just overwrite the current install of Ubuntu. Just be sure to choose the same partition for / (root) as your current one & its format ext4. It should find swap. If you have the separate partition for /home choose it also. If you have any data you want saved DO NOT reformat it.

https://help.ubuntu.com/community/GraphicalInstall