Your old 3.5-inch HDD can be housed in this 3.5-inch HDD enclosure.

To clone your existing OS/app setup first, purchase a cloning cable or 2.5-inch HDD/SDD enclosure to connect your new SSD to your mac, then use the Super Duper app to perform the clone, then switch the drives.

Plus, you’ll need to add in the OWC Adaptadrive 3.5-inch to 2.5-inch drive converter.

To upgrade the factory 3.5-inch HDD to an SSD, purchase any 2.5-inch SSD along with the same Hard Drive Upgrade kit.

If you have a ‘Fusion drive’ setup, then you’ll need to split the fusion drive first and then perform the clone operation before upgrading the HDD.The enclosure can also house your old HDD. To clone your existing OS/app setup first, purchase an external 3.5-inch HDD enclosure or dock and put your new HDD in it, then use the Super Duper app to perform the clone, then switch the drives.To upgrade the existing HDD, purchase a larger 3.5-inch HDD along with the Hard Drive Upgrade kit. At the time of purchase, Apple offered a 1 TB or 3TB 'Fusion Drive' (which combines a 128GB ‘blade’ SSD and a 1TB/3TB hard drive), or a stand-alone 256GB/512GB/1TB blade SSD.

The iMac 27-inch Late 2013 models have a 1TB 3.5-inch factory HDD with a 6 Gb/s SATA port.Follow this guide to install the RAM modules. To install the RAM, you'll need a Spudger.

Late 2013 imac maximum ram