Open the Enterprise manager. Go to the server group (you'll see the
registered sql-servers), right click and choose properties.
You'll find information on how to set the memory amounts, cpu use etc.
Furthermore press F1 and it will guide you how to change the sql-server
settings through the option 'properties'. You need to read and search
through the above context to find some answers because many
options/solutions are based on the hardware you use and the replies we might
give you, could be wrong or ambiguous. As Kevin said it's a very big issue
to cover here.
Paradox' yesterday, where I had some questions on performance. Some of the
replys I got is that I can also change some settings on Sql Server itself
that will improve performance.