Knock sound in engine

Hi all, I hope I'm in the right forum / category as I am new to this group? Ihave a 2009 Fiesta Ambiente 1.4. I have read through all the comments based on oil pressure warning related problems and it seems that I could be experi ncing the same with mine. I have to admit that the engine was really poorly maintained in terms of service intervals and oil changes. The problem I'm having now is that the red oil light came on about 3 days ago so i drove the car home, travelled about 3 kilometers and left it over the weekend. Spoke to a mechanic regarding the issue and he came over to do an oil pressure test for me. Specs on the car shows that the minimum oil pressure should be 2.5 bar and the test revealed a pressure of almost 4 bar. So in terms of pressure all seemed ok and hopefully the warning could be a faulty sensor? Apart from the oil light warning and low oil pressure warning on the display, the engine is making a noise sounding like a bearing knock, although the noise sounds like it is coming from the top. So could this be a sticky lifter or in fact a bearing knock? Based on most of the comments posted regarding this issue it seems a good idea to change the oil pump, filter and oil. Just concerned about the knocking noise. Haven't had any loss in power at all so far. Should it turn out to be a bearing knock can and should the big ends just be replaced, in addition to the other parts ie, oilf pump, filter and oil? Many thanks