1) Go to the e-mail tab.
2) Choose "Menu" in the lower right-hand corner.
3) Choose "Accounts"
4) Choose 'Accounts..." (redundant, I know).
5) A list of your e-mail accounts pops up. This is the hard part: Tap the account you want to alter, and instead of opening it, drag your stylus (or finger) off the edge of the screen, so that it's highlighted but not opened.
6) Choose "Menu" in the lower right-hand corner.
7) Choose "Options"
Again, choose the account you want to alter.
9) Select "Send/Receive Schedule"
10) Here it'll say "Every 2 hours." You can tell it to check as often as every 5 minutes.
11) Once you've selected what you want, hit "done" and then "done" again. You might want to restart the phone to make sure it takes effect.