In SQL Server Enterprise Manager and change one of the columns and save it, it will create a table with the new definition, and copy all the data to that new table, and then delete the old table when it's done.
But if your table is large (let's say on the order of 100GB), it can take a long time to do this. Even worse, if you don't have sufficient disk space, it doesn't notice ahead of time, and it will spend a long time trying to copy the table, run out of space, and then decide to abort the process.
We have other ways to copy the data in smaller chunks, but those require significantly more manual intervention, so it's usually easier to just let Enterprise Manager figure it out, as long as there's enough disk space.
So for a long running "Design Table" save like this, is there any way to cancel once it's started? Or do you just have to wait for it to fail?