They're not too hard to replace. Just get new injector seals and a gasket from a Volvo dealer. It's pretty straightforward job. You just remove the fuel rail,injectors and turbo/vacuum solenoids.
Make sure you keep the injectors in order 1/2/3/4 as they're coded, and don't overtighten the fuel pipes
I usually leave the fuel hardlines connected to the fuel rail and just undo them at the injectors and fuel pump
The solenoids just kinda slide out of the rocker cover
https://youtu.be/xmsCX77ZDx4