Upgrading old design computer

[TheSilentHawk]

I have a computer that I got back in 2013 that I have been using for 3D design. I thought it would last a lot longer but as my designs got more advanced so did the load on my little system. I have built my desk around the computer and would like to upgrade it as much as possible before I have to build a new one.
My primary questions are:
What is the best CPU it can run?
How much RAM can I cram into it?
What are the best Graphics/Video Cards it can run?
Here are the specs:
HP Pavilion Slimline 400-000 Desktop PC Series
Joshua-H61-uATX
uATX - 24.4 cm (9.6 inches) x 24.4 cm (9.6 inches)
Intel H61
2 x DDR3
Front side bus speeds: 5 GT/s
Processor socket: LGA 1155
Expansion Slots:
•1 PCI Express x16 (Gen2.0)
•3 PCI Express x1 (Gen2.0)
•1 PCI Express Mini Card x1\
Full List Here:
HP Pavilion Slimline 400-034 Desktop PC Product Specifications | HP® Customer Support

 

[Joe C]

For 3D design an i7 3xxx would work for that board, but you might get away with an i5 cpu.
The max memory that board can handle is 16 gb with 2 DDR3 slots on the board
On board graphics, should have a discrete GPU, but that pathetic case doesn't look like it could handle a good video card and you'll also need a better power supply, you have a 220 watt micro-type of power supply.
You'll need to get a better case and power supply, Keep the board and replace every thing else?

 

[PP Mguire]

How do you build a desk around a small form factor machine? That doesn't make much sense to me.

Max memory you can put in there is 16GB, best CPU is i7 3770. You need a GPU that can take some of the GPGPU load off the CPU. Unfortunately due to being SFF your options are very limited. The best GPU you could get is this but the cost might outweigh the advantages for 3D work. Your best upgrades will be RAM and CPU.