How do you sew name tapes on ACUs?

Spend the 5 bucks and take it to a professional -

Wow from the comments I see we don't have anyone who sews here! Check it out, get a seam ripper SSGT Josiah Brainard was on the right track, but they are extremely sharp so be careful not only for the uniform but also your fingers! Double check your regs, but if allowed there is a seamstress glue out there that is waterproof, it's just like superglue for people who sew. Just check your regs first to make sure it's allowed- if so, measure twice glue once and you are done.

For removing the velcro, use a seam ripper. https://www.walmart.com/ip/Singer-Seam-Ripper-and-Tape-Measure-Combo/24663550 That will allow you to cut the stitches while greatly reducing the chances that you cut your uniform. I will not guarantee it, as I have not actually sewn anything on the multicam uniform, but I believe the thread color you are looking for is Tan 499.
http://www.ebay.com/itm/499Tan-Thread-Military-Sewing-Nylon-Bonded-T90-16oz-Spool-Fabric-Multicam-Camo-A-/ [login to see] 21

Check Youtube for some tutorials, and try sewing some old ACUs before you risk trashing your OCPs tops.

As far as removing the hook and loop fasteners from the uniform, a sharp knife and patience are all that is needed. Start at the corner, fold the corner back and slide the knife against the thread. It will cut the thread, then pull on the hook and loop strip and it will pop the threads to the end. Then just cut the threads on the end and you are done. The uniform is where the patience comes in. If you are not careful you can cut the uniform.

Look in 670-1 on where the name tapes are to be located on the uniform. If you use fabric chalk or a fabric marker you can mark (or trace) the place where the original hook and loop tape is. place it between the marks and you are done.

Please do not! Professionalism reigns! I sewed my 'mosquito wings' on once! Never again!

When you remove the rank portion of hook and loop tape, you have to be careful as the zipper runs through the middle and the hot mess is all intertwined. You will have to re sew the zipper. I admire your grit on this, but unless you have access to a heavy duty sewing machine, I would dissuade you from sewing on your own items unless you have done it before/know how. The string is actually thread.

Removing the old Velcro is easy. Seam ripper. Recommend against using a razor blade or knife. You need to place the name tapes over the old Velcro spot (you can see where it was stitched). I removed all my Velcro components to defray the cost. They charge like Three bucks a patch. The sew shop usually takes the patches and cuts, folds and boxes off the tapes and qualification badges (by sewing them that way by them selves), press them with an iron, then sews them to the uniform. Would strongly advise against doing it by hand as it will look like a hot mess unless you are that good. Most ain't.

Use a seam ripper to remove the hook and loop tape. Once that is completed I use a product called seam witchery. It is a white tape like roll that you can get at the PX. Finally cut a piece and place it in the spot where the hook and loop tape was. Place the name tape using the old stitch marks as a guide, measure placement, and iron it on. Let it cool then sew it on. The seam witchery will hold it in place long enough to take your time and sew it on. As for thread color, I have uniforms with camel and olive colored thread. So just match the stitches on the pocket like I read in other comments.

2LT (Join to see) Alterations shop is my recommendation to you for sewn on rank. You can also save a few dollars if you carefully remove the hook and loop fasteners yourself. Let the experts do the rest for you unless you are good a sewing and making it look professional in appearance.

I'm debating doing this when I make Specialist, at least for one or two sets. I'm not confident in my sewing abilities outside of minor repairs so I think I'll just pay to have them done.

On a side note, is there a problem with ironing ACUs? I've been doing it lately to the pockets and collar to keep them looking sharp like when they were issued now that they're starting to curl. I've gotten some mixed responses.

you're Kidding Right...
as we cant use Velcro because it's a violation of paten and Copy Right infringements ...
Its called Hook and Pile Tape...
and you put the Hook portion on the Back of the name tape and sew it on or use upholstery Glue
and I have been retired for 18 years...