Hi Gabriel,
Start Windows and shutdown Windows virtual machine from Mac menu Actions > Shutdown or Stop refer to this article for more information.
Then try increasing memory followed this steps.
Let us know if this help?
Nope , I move it to the right up to any number (say 4 GB) , and as i release the click , it immediately goes back to 2 GB , same if I put 512 MB , goes again to 2048...
GabrielP3, try to create an empty Virtual Machine and Map the existing Virtual Machine Hard Disk by referring to this article & check if you are able to adjust the memory.