Should I build a PC or upgrade my prebuilt Lenovo H535?

Build a new machine. No way you'd want to bother from upgrading from an APU.
This should cover your needs. Unless... You also want another keyboard and mice. Do you?

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i3-6100 3.7GHz Dual-Core Processor ($110.99 @ SuperBiiz)
Motherboard: Asus H110M-K Micro ATX LGA1151 Motherboard ($56.99 @ SuperBiiz)
Memory: Corsair Vengeance LPX 8GB (2 x 4GB) DDR4-2400 Memory ($34.98 @ Newegg)
Video Card: EVGA GeForce GTX 950 2GB Superclocked+ ACX 2.0 Video Card ($119.99 @ Newegg)
Case: Corsair 100R ATX Mid Tower Case ($39.99 @ Micro Center)
Power Supply: Antec EarthWatts Green 380W 80+ Bronze Certified ATX Power Supply ($42.99 @ SuperBiiz)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($83.89 @ OutletPC)
Total: $489.82
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-06-01 23:37 EDT-0400
 


Thank you so much for the quick response! I do not need another keyboard and mouse, but I will need a wireless network adapter because I don't have access to ethernet. Also, is it hard to build a PC. I am 16 and I do not know the difficulty of building one.
 
x)
Let's see what I could do...

Aha!
PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i3-6100 3.7GHz Dual-Core Processor ($110.99 @ SuperBiiz)
Motherboard: Gigabyte GA-H110M-A Micro ATX LGA1151 Motherboard ($49.99 @ NCIX US)
Memory: Corsair Vengeance LPX 8GB (2 x 4GB) DDR4-2400 Memory ($34.98 @ Newegg)
Video Card: EVGA GeForce GTX 950 2GB Superclocked+ ACX 2.0 Video Card ($119.99 @ Newegg)
Case: Corsair 100R ATX Mid Tower Case ($39.99 @ Micro Center)
Power Supply: Antec EarthWatts Green 380W 80+ Bronze Certified ATX Power Supply ($42.99 @ SuperBiiz)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($83.89 @ OutletPC)
Wireless Network Adapter: Rosewill RNX-N150PCe PCI-Express x1 802.11b/g/n Wi-Fi Adapter ($8.99 @ Newegg)
Total: $491.81
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-06-01 23:54 EDT-0400

At least... Good thing is, the wireless card is based on AR9285. Awesome little thing, if you don't mind the lack of 802.11ac.
 
PCPartPicker part list / Price breakdown by merchant

CPU: Intel Core i3-6100 3.7GHz Dual-Core Processor ($110.99 @ SuperBiiz)
Motherboard: MSI H110M Pro-VD Micro ATX LGA1151 Motherboard ($47.98 @ Newegg)
Memory: Kingston 8GB (1 x 8GB) DDR4-2133 Memory ($26.99 @ SuperBiiz)
Storage: A-Data Premier SP550 120GB 2.5" Solid State Drive ($34.99 @ NCIX US)
Video Card: MSI GeForce GTX 950 2GB Video Card ($139.99 @ Newegg)
Case: Rosewill SRM-01 MicroATX Mini Tower Case ($27.99 @ Amazon)
Power Supply: EVGA 430W 80+ Certified ATX Power Supply ($32.74 @ Amazon)
Operating System: Microsoft Windows 10 Home OEM 64-bit ($84.99 @ NCIX US)
Total: $506.66
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2016-06-01 23:55 EDT-0400

similar to okcnaline's build. Slightly over budget, I went with a less power supply, case, motherboard and Ram, I saved enough for a 128 GB SSD, for your OS and most used programs. Like ocknaline, I suggest reusing your 1TB drive. the PSU is NOT top quality, but I'm also sure it won't just up and die on you either, especially with the low load this build produces (just 212W)
 
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