If I were you, I'd check out "man chown". This tells you all you need to know.
You could also consider "man ls"... For how to list files/directories in a folder...
But I'll also provide you with the info you need:
1. ~# cd /opt
2. ~# ls -lh
Command 2 will list all files in /opt, with permissions/owner/group. And displays them with "human-readables", which means size of file will be in kb/mb/gb instead of bytes.
Now that you have the list, let's change the owner to root (make sure you're logged on as root or use "su -" or just "su".
3. ~# chmod -R root:root xboard-4.2.7/
The above command will change the owner and group to root and root. (chmod <user>:<group>).
"-R" means the command will be recursive, so it will change owner/group on all files and subdirs in the "xboard-4.2.7" directory.
PS! Just to clarify: Root can change owner on all files (even if there's no existing owner like when you see the owner ID: 541, instead of the owner name), so NO you're not screwed.
Just make sure you change ownership to an existing user/group.
You should also make sure you are in the right directory before you try to configure: "cd /opt/xboard-4.2.7/".
Most linux distros I've encountered also has something called bash completion, so you can usually just type:
~# cd /opt/xbo<TAB>
Where "<TAB>" is the Tab/Tabulator key (2 times). The first time you hit tab (if there is only one file/directory that starts with "xbo") it will complete the typing for you.
The second time you hit tab, bash will list all files/folders that start with "xbo".
Hope this clears up a few things? If not? I need a translator