in reply to
Program size and effeciency.
They have given me a older project to take care of and to clear bugs in them.
Start from the bugs. Clean up as you go, and only so much as you need to.
Resist the temptation to start from scratch, because you'll get blamed for whatever new bugs you introduce. Remember that you'll find a lot of seemingly non-sensical lines of code - but each was put in for a reason, and some may be crucial. Until you are very familiar with the problem at hand don't assume you know all the wrinkles.