I am starting to run out of disk space. How can I check where all the largest files are located on my Ubuntu installation so that I can delete them?
You can use Disk Usage Analyzer (installed by default in Ubuntu). To use it just search Disk Usage Analyzer on dash (note that your icons may be different)
And then select the disk you want to scan. You will get a report similar this one
If you are using a CLI installation (ex: a server) or just prefer to use the terminal, you can try