What do you consider a "very long time" for the update?   What are the specs
on your system, to include the CPU rating, hard drive total/free space
reported, amount of RAM installed, and if the system is on a LAN (and you
have mapped drives)?

Regardless of the above, the primary factor in installing an update is free
space on your local hard drive.  You can help by cleaning up the system;
here are some steps to start with:

1. Clean out your default Temp/Tmp folders.  The default Temp folder should
not be used to store personal files, and should be cleaned out regularly.
2. Clear your IE TIF (Tools/Internet Options/General tab/Delete files, then
select to clear Offline content).
3. Open My Computer, select the C: drive, right-click for Properties, then
Clean Up.  Repeat for all local hard drives.
4. Find and remove any folders named "WUTemp" on all local drives.
5. Run a full disk Scan and then Defrag on all drives.

You can also move or remove programs you no longer use/need to free up
space.  As a rule of thumb you should always have 20% of the total drive
capacity free. (As an example, for a 30GB partition you would want to keep
at least 6 GB free at all times.)