I'm assuming you're rooted. Updating radios can keep help your phone when it comes to coverage. Either it be normal use, roaming, 3G, 4G or whatever the case maybe. Another good thing to do is after updating your radios is to update your PRL.
First download the radio
[ Radios ][ 9-5 ] All EVO Radio, WiMAX, PRI, NV & HBoot versions - xda-developers.
If you rooted when on the 4.24 then you have the current wimax, nv and so on. Just need the radio.
I use Amon and here is how it goes.
I wipe cache and dalvik cache.
Not data
Flash like you would a kernel, but it will ask for you to reboot. Go back to main menu and reboot.
You'll screen will go black.
You'll get an image of a phone with two arrows going in a circle motion with a downward arrow (still image. Not really moving)
Give it awhile.
When done you will do a second reboot and it will reboot as normal.
Important: Make sure you have 30% or more of battery and NEVER PULL YOUR BATTERY. THIS IS A SURE WAY TO BRICK YOUR PHONE.
When back to your homescreen go to your settings -> about phone and look at your baseband version to make sure it went.
Here are screenshots of it.