In the BIOS, locate the MB Intelligent Tweaker M.I.T. section. Click on CPU Clock Ratio and see if you can change the setting from Auto and enter the higher setting of x14. Click Save and Exit, then check if the computer restarts and boots into Windows. Run a few stress tests to check overclock stability.
The default multiplier for the 5200+ is x13, which gives a clock speed of 200x13=2600MHz.
If setting x14 in CPU Clock Ratio works, your CPU will be clocked at 200x14=2800MHz.
The 200 figure is the FSB (Front Side Bus) speed.
https://www.cpu-world.com/CPUs/K8/AMD-Athlon 64 X2 5200+ - ADA5200IAA6CZ (ADA5200CZBOX).html
If the x14 multiple is stable, you could try x15 (3000MHz).
If the system crashes, enter M.I.T. and locate System Voltage Control. This is where it gets dangerous. See if you can increase the CPU voltage a tiny amount, e.g. 50 or 100mV (0.050V or 0.100V).
Reboot the system and see if it's more stable with additional voltage.
WARNING. If you add 500mV (0.5V) by mistake, you'll probably see "magic smoke" rising from your CPU, as it dies instantaneously from gross voltage overload. Over enthusiastic overclocking leads to dead components and disappointment (or despair).
N.B. the 5200+ nomenclature comes from AMD's claim their Athlon clocked at 2600MHz performs similarly to a CPU running twice as fast, i.e. 5200MHz or some such nonsense. It's been so long, I forget the exact reason.
If you get really stuck, I'll dig out a similar Athlon Socket AM2 rig and see what's possible.