Well sorry for telling you RTFM, but honestly I (like most people I would think) don't know all options by heart and would have to look them up anyway. So why don't you read the man page?
The parameter is, unsurprisingly, named "size". You can use it to find files that are larger or smaller than the provided size, or the exact size. Something like "-size +5GB" in your case. Read the man page to double-check. I told you already how to search inside a man page.
You also want to delete those files. One way to do this is adding the "-exec rm {} \;" option. This is inefficient if you find many files, since you start up the "rm" program each time a matching file is found, but I don't think you have too many 5GB files.
And I would agree that the syntax is ugly.
If you expect that many files match the search criteria, you are better off with running a single rm command and give it the list of all files:
Code:
rm $(find -whateverfilesyouwanttoselect)
Now the problem is that you might have more file that fit rm's parameter list. In this case, use xargs:
Code:
find -whateverblabla | xargs rm