According to the page created by the developers on Jul 24, 2013, these are the system requirements for that time to properly run Parallels Desktop on your Mac:
Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor (Core Solo and Core Duo processors are no longer supported)
Minimum 2 GB of memory (4 GB of memory is recommended to run Windows 7 in a virtual machine or if your host OS is Lion)
About 700 MB of disk space on the boot volume (Macintosh HD) for Parallels Desktop installation
About 15 GB of disk space for each virtual machine
Mac OS X Mountain Lion 10.8, Mac OS X Lion 10.7.4 or later, Mac OS X Snow Leopard 10.6.8 or later.
Note: Mac OS X Leopard v10.5.x is not supported in this version of Parallels Desktop. Note: Parallels Desktop 8 for Mac is a 64-bit application.
To see them for yourself, access the following URL. Also, the latest version of Parallels Desktop is 13, and if you plan to use it, make sure to download it.
You can upgrade the MacBook to another version through the App Store or using the Apple logo > Software Update. You can do it with the Parallels Desktop installed, but first you need to make sure that you have the virtual machines exported and available, because you will also have to update the Parallels Desktop as well. Luckily, the latest version of Parallels desktop is compatible with the latest version of OSX El Capitan.
You need to pay before using or u can to download payed version from browser
According to the page created by the developers on Jul 24, 2013, these are the system requirements for that time to properly run Parallels Desktop on your Mac:
Note: Mac OS X Leopard v10.5.x is not supported in this version of Parallels Desktop.
Note: Parallels Desktop 8 for Mac is a 64-bit application.
To see them for yourself, access the following URL. Also, the latest version of Parallels Desktop is 13, and if you plan to use it, make sure to download it.
You can upgrade the MacBook to another version through the App Store or using the Apple logo > Software Update. You can do it with the Parallels Desktop installed, but first you need to make sure that you have the virtual machines exported and available, because you will also have to update the Parallels Desktop as well. Luckily, the latest version of Parallels desktop is compatible with the latest version of OSX El Capitan.
Official website of Parallels Desktop: http://www.parallels.com/eu/products/desktop/
Apple Support page: https://support.apple.com/en-us/HT201541