Bar change newbie.

Why is everyone giving tips about wrapping bars...that wasn't what she needed advice on...anyone she's made a marvellous job or changing the bars and wrapping them from the picture I just saw

In my first few attempts at wrapping bar tape, I didn't do the first revolution of the wrap right enough which makes it difficult later on to plug the end cap in. Soy advice would be to make sure the first wrap is quite tight so the natural stretch in the tape pulls the bit of overlapping tape inwards.... If that makes any sense. There's a good video on youtube by the GCN boys where they have some Italian mechanic showing you how it's done. The rest is fairly straight forward so long as take your time. Oh year one more thing, snip the end of the tape with a scissors diagonally when you get to the end. This will help tape it to the bar.

Park Tools have the best tutorials online I find.
You'll be better marking the shifter positions rather than a picture, it'll take an age to get back other wise and if the hood shape is different it won't look 'right'.

Unwrap the 49 bar tape, then peel the shifter rubber back to access the clamp screw. Undo this just enough to slide the shifter down the bar and off. You won't need to release your cables for any of this. Unbolt the stem plate and swap bars, then do everything in reverse to finish off.

What 40 bars are on there at the moment? Because as I said up there earlier, Deda measure centre of the tube to centre so their 38 bars are exactly the same width as, say, a Ritchey 40. If the shape of the drop is the same then you might not even need to do any of this.

If you do swap, the housings should be more or less the same length so I wouldn't worry about that if you don't want to get into undoing cables, but just make sure you know how you like your bars set up. Maybe take a picture of them side on so you can replicate the bar rotation and shifter position more easily.

The best wrap job I ever did was my first one, I didn't waste any rolls either so don't expect to need a half dozen backups after you balls it up because you won't. I really took my time on that attempt so it was meticulous, now I just wrap them without caring too much and end up with a tiny gap under the hoods but only I know it's there.

Deda measure centre to centre so a 38 is the same as another brands 40 measured outside to outside.

I ride a 40 Ritchey so the same size, and I'm a 6 foot tall dude. Smaller the better. Adam Hansen uses some custom 36s IIRC.

Watch a few videos to see if you feel up to it, it's not all that hard to do in honesty. Or might need to trim the cable housings a bit if the bar shapes are different enough to warrant it. Just make sure the STIs are bolted on at the right position for you before wrapping the bars.

Rather than asking on a forum, surely you can ask a friend to help you? Its one of those things that isn't that hard but just takes a little time.

Check out youtube on how to change a stem, how to wrap bar tape. how to attach shifters to handlebars and you should get how to do it all. With new bar tape, have a practice wrapping without taking the backing of the sticky strip to get a feel so you dont have to go through a few packs of tape. You shouldnt need to recable.

And 38cm is very small. Im a mid height size 8 lady and ride 40-42cm on road bikes.

Sticking with the 40cm bars fitted will not do you any harm to be honest. Bar tape has a nack to it and it's not something I would recommend for a beginner, it's not that it can't be learned I just wouldn't want you going through several sets of tape before you get it right. Unless you really are tiny I don't think 38's offer much other than a rather hunched up position that is uncomfortable, it's hard to go too wide with bars but it's easy to go too narrow and injure yourself. Leave the tape in place and remove the cables from the outers and you will most likely be able to simply unbolt the shifters from the band on while leaving the band on in place and put the Ultergra ones on instead.