i guess you have dropped all the settings to low on both them games. if so and you still get lag then you can assume that your lappys ability to play games is very limited... try some less demaning games install steam and start downloading the game demos. this will give you a better idea of what your system can handle and it wont cost anything other than bandwidth and time.
you have 48 texture alu's which means very low end entry level gaming for medium demanding games like the sims, rollercoaster tycoon. you should also be able to play cod4 on reduced settings. but some maps may be unplayable even at low. other fps shooters like fear and stalker may run ok at reduced settings and rez but really your selection of playable multiplayer games will be quite limited.
best stick to single player...
You can see that your GPU has only 50% of the shader cores as the 525m (which is identical to the 550m with a lowered clock).
You can try to Overclock the GPU with something like afterburner, but watch the temps and keep in mind that you will only see 50% the benefit, that, for example, the 525m would as you are running half of the number of compute resources.
I would be thinking that the 520m might just (if you are lucky) be the same GPU as the 520MX which simply has higher clocks (same number of shaders). So a realistic target for an OC would be approaching 900MHz.
WATCH THE TEMPERATURES. Cannot stress this enough. 85C is a realistic limit at full load, any higher and abort and clock down.