You're on a hard-tail mountain bike - it is never going to be "fast" but can be faster.
Easy or free changes:
- If your suspension fork has a lockout lever, activate it when conditions don't require suspension, ie road riding. This reduces energy lost to actuating the suspension when it could be going into forward motion
- Clean, wash, and service the bike. A dirty bike is slower than a clean bike, and a correctly lubed bike is faster again.
- Inflate your tyres - for road riding they should be a bit harder than off-road riding. Can't say exactly, but try increasing the pressure a bit and see how it rides. Go too high and the handling will drop off and get squirrly.
- Check the weather forecast - ride with a tail wind and you'll be faster!
- Carry less stuff - if its not likely to rain, carrying a jacket is a extra mass. If you don't drink through a whole bottle of water, just take one.
Pay to play:
- Upgrade the tyres to something thinner and smoother. Your current tyres are "anti puncture" and that tends to increase the rolling resistance. Downside, more punctures and you lose some of the off-road grip when in dirt and shingle.
- Aerobars - if your average speed is up above 30 km/h then aerobars can help reduce air resistance. But they're unsafe in traffic and when manoevering a lot because the hands are so far from the brakes.
Free but hard work
- Lose mass off the rider - this is particularly challenging, but 5 kg / 10 pounds can make a world of difference. I've added that much lately and definitely notice a drop in times.
- Add training, practice, and experience. Regular riding will slowly improve your base performance which gives more power and therefore better speed, and more endurance at that higher speed.
Structured training will help bring around improvements faster, at the cost of time and effort.
- Replace/supplement the bike with another. It is a very nice hardtail MTB, but it will never be fast. The replacement might be a road bike, or it might be electric-assist.
Your initial request about changing gearing is not unusual, but most cyclists only have so-much power on tap, and changing gearing isn't going to do much for someone with 100 or 200 watts. The Pros can put out 400+ watts for an entire hour, so for them a chainring of 50/55 teeth and an 11 tooth rear might be ideal.
If you still want to change gearing, then try and work out what you DON'T need. For example, if you never ever use the little chainring, then why have it? You could go from the 30/46 to a 40/53 and not miss anything, if it fits on your frame.