- Processor 2.3 GHz Dual-Core Intel Core i5
You have the crippled "educational/institutional iMac with a slow laptop 2-core processor instead of the more capable 3.0mHz 4-core processor used in standard 4K iMac 27-inchers. It is never going to be fast.
The others are right: you have RAM slots but accessing them is a Pro job that require gutting the computer with the risk of damage to delicate parts. Even finding an Apple Authorized Service Provider or independent provide to do the work is not simple because some choose NOT to work on sealed-case iMacs. A local provider who will do the work told me he has the charge at least two hours labor on top of the cost of the RAM and a reseal kit. His labor is US$80/hour.
On top of that, adding any amount of RAM—other than a waste of money—would make no difference in apparent speed. 98% of all slow iMac complaints here turn out to be the slow and under-spec 2.5-inch laptop drives Apple chose to install as the base storage in all 2012-2019 21.5-inch iMacs.
One test is simply answering three questions:
- is the computer slow to boot?
- Are many apps slow to launch
- Once launched, do apps seem to run fine?
Three "yes" responses point accusingly to the well-known slow hard drive. A sequence of "yes-yes-no" answers could indicate something else but will need further testing. Let us know. You may still have cost-effective hardware options.