Unlike in previous versions of Xcode accessing performance tools aren't straight forward in Xcode version 4. But if you follow the following steps, you would do just fine.
1. Go to edit schemes
2. Select Profile from the list to your left
3. Set the build configuration to debug
4. Select the instrument you want to run from the list (or select ask on launch)
5. Click ok
6. Click and hold the run button and select profile. Instrument will launch according to your configuration in step 4 (or press keys ⌘I).
Note: configuring schemes is a one time thing.