You need to know what diameter your current fork’s steerer tube is. They come in 1 1/8, 1.5 and tapered.
For a straight swap you need a fork with the same steerer. However, depending on your frame’s headtube (again there’s a range of options) you may be able to use a different type of steerer, but you will need a new headset if you do.
If you swap to a QR or 15mm axle you’ll either need a new front hub or, if your existing hub can be adapted, a set of adapters to suit the new fork.
Why do you want to upgrade? Your existing fork should be pretty good