If it was already at 1024 MB, you might put in 1536, or 2048 MB. Normally it should have 1GB (1024MB) of memory allocated, but sometimes it'll need more.
Also, when it talks about memory, it means RAM, not your hard drive (Or SSD.)
1536 MB = 1.5 GB
2048 MB = 2GB
I've dealt with this issue before, and the easiest way that I found was actually a mod out there, but that doesn't seem to work for everyone.