Go to the control panel, find Windows updates and allow MS to download and install the updates as needed. That is if you need to do an inplace upgrade.
If not, choose the custom option to do a clean install, that's the best way to go anyway.
Remember to backup first, use the W7 Easy Transfer Wizard to save files and settings. To use it, insert the W7 DVD
Open Windows Explorer by right-clicking the Start menu, and then clicking Explore.
Browse to the DVD drive on your computer and click migsetup.exe in the Support\Migwiz directory.
The Windows Easy Transfer window opens.