This is your processor: Intel® Core™ i3-540 Processor (4M Cache, 3.06 GHz) Specifications
For memory specifications, refer to section 1.1.1 table 1 on page 9 of the technical specification for your board: https://downloadmirror.intel.com/18505/eng/DH55TC_TechProdSpec.pdf
For 8gb memory, you would probably want to use four 2gb sticks that meet the specifications defined in the above document.
However, you are using Windows 10.
You should note that your board is not supported on Windows 10: Supported Operating Systems for Intel® Desktop Boards
You should also note that your processor is not supported on Windows 10: Intel® Processor Support for Microsoft Windows® 10
And, your onboard graphics are not supported on Windows 10: Supported Operating Systems for Intel® Graphics Products
Your board can handle two pairs of unbuffered, non-ECC, x8 organized, 5V DDR3 DIMMs. Note the following:
- Recommendation is to use 1066 or (better) 1333 MHz. Faster DIMMs can be used, but problems/incompatibilities may occur.
- Each individual DIMM can be 1, 2 or 4 GB in size. Maximum supported is 16 GB total.
- All four DIMMs should have identical specifications. Though the size of the DIMMs used in one channel may differ from the other, it is best if they are all the same size.
Here is a link to a summary of the general requirements and a list of known-compatible memory: System Memory for Intel Desktop Board DH55TC. This list is pretty old; you will likely need to match available DIMMs against the specifications for the listed DIMMs.
Hope this helps,