Apers, do NOT delete anything - no matter the size. Important game files are a lot larget then 40KB... also, file size has little to do with lag.
Things you can check:
- are your graphic settings the same? For some people installing the patch changed some graphic settings back to default.
- defrag your HDD (where the game is on)
- make sure your firewall allows AH again (new version needs to be reallowed!), or turn your firewall off to see if that helps with lag
- Antivirus: Same as Firewall. Some AV programs check every packet that leaves or is recieved by your computer. This can cause severe lag issues
If none of that helps. well need a dxdiag report to be able to help you further.