Each retail manufacturer sets the BIOS screens up a bit different with different headers, but I can give you a generic "what to look for". Judging from your question, I am guessing that you already know how to access the BIOS setup screen in your computer. There will be a header which may be titled, "boot", "Boot Setup", etc. Sometimes under the old American Megatrends BIOS screens the boot order is found under the Storage Drives section, with other BIOS screens it may be different. I will use a Phoenix BIOS for an example. In general, here is what you do:
1. Restart the Computer and enter the BIOS Setup Utility; this is done by tapping a key repeatedly, usually the DELETE key (but not always).
3. Locate and Navigate to the Boot Order Options in BIOS
4. Make Changes to the Boot Order
5. Save Changes to the BIOS Setup Utility
6. Confirm Boot Order Changes and Exit BIOS
7. Start the Computer With the New Boot Order
I will use an example (I hope this website allows multiple pictures to upload, but here I go):
The first screen will look something like this, with a general posting of your components:
Tap your right arrow key
to move this hilight over to the "Boot" header in the top, blue header bar (as below):
Now you have to figure out how this manufacturer set it up; usually guidelines are in the right column to help you, but the general rule is that you hilight the hard drive and (somehow) move it up to the top for the first boot device. Sometimes you hilight "Hard Drive", then press "Enter" and it gives you more options for moving it to 1st boot device. Other times you may be able to directly move it from this screen (above) by pressing a different key. Just work with it and eventually you will figure it out. If you still have the original manual that came with the computer they may (or may not) give detailed instructions.
When you finally get it configured, be sure to save it. This is usually done by pressing F10 key, it will ask you if you want to save settings, press Yes and you are done. If you need additional help, I hang out with a bunch of other techs at the (free) compute help forum, www.suggest-a-fix.com This website is not set up for easy back n' forth communication. Hope this helps you.