It is absoloutely possible to DIY plumbing in most cases, but it pays to take some time to fully understand the situation before you start.
The first thing I would do is evaluate the broader situation.
- What does that valve feed?
- where is it fed from?
- Is there another shutoff valve upstream?
- Does the upstream shutoff valve work?
- Does the upstream shutoff valve require special tools to operate?
- what else does the upstream shutoff valve shut off? if push came to shove can you live without it for a few days?
Unfortunately your existing valve is soldered in, which makes replacing it non-trivial. So I would probably start by investigating the repair options Ecnerwal has mentioned. However, before I started I would want to have a plan in place for what I would do If things go wrong and I had to switch strategies from repair to replace.
My replacement strategy would probably involve cutting the valve out and fitting a new valve with compression fittings. Unfortunately cutting the valve out will probably leave a gap too long to fit a new one, so it would probably be necessary to cut out a longer length of pipe and then fit a new section of pipe and a coupler.
Looking at your other posts it looks like you are in the USA, while I am in the UK. So the exact products available may differ. Depending on how much play is in the pipes it may be difficult to fit a regular coupler. In the UK you get special "repair couplers" that are longer than a normal coupler and only have a depth stop at one end, so you can slide them onto one pipe and then back onto the other one. I'm not sure if similar products are available in the USA.