Unable to free up enough space (1.5 GB at least) on your hard drive.
at least 也可换成 minimum.不过一般都不这样说,而是分开成两句话：
The minimum hard disk requirement is 1.5 GB.xxxx is unable to free up enough space on your hard drive (或者 on hard dirve C:)
这里的xxxx是某个程序或应用的名词.