handlebars, shifters, derailleurs, hydraulic lines...likely you will need longer lines...handlebar tape and that should do it.
If you feel you are a bit lower than you prefer you can either flip the stem if that raises it or replace with one that angles up to give a more comfortable position.
While you're at it you should replace the hydraulic fluid...just to give it a good flush and have new fluid in the lines...may as well considering the work you will be doing.
May as well replace the shifter cables and housings as well...
Cross compatibility of the drive train may be a problem but since you give no details on the system no info is offered thus full replacement.
The brake calipers should work with any hydraulic brifter.