The page https://doc.tiki.org/Installation describes two ways to get the tiki files onto the server.
I tried svn but that broke off in the middle then went the second recommended route transferring the data via ftp. While this works it sure takes very long to finish because each file is transferred separately.
Here is a much faster way that I finally went with. You need an ssl connection to the remote server.
Navigate to the public_html folder of your apache installation. Make sure the folder is empty.
Now get the the zip archive
$ wget https://sourceforge.net/projects/tikiwiki/files/Tiki_18.x_Alcyone/18.1/tiki-18.1.zip
Unzip the archive
$ unzip tiki-18.1.zip
Move the contents of the unzipped tiki folder on level down to the public_html folder
§mv tiki-18.1/* ./
Finally remove the downloaded zip file and the empty tiki-18.1 folder.
That's it! Continue with step 1.4 of the installation guide.