There are many tools and tricks to help make your sounds brighter. I'll list some plugins below than can be used to get a thicker, warmer sound.
~Reverb~ self explanatory. Making your sound less sharp, and raw.
~Mono/Stereo width plugins~ simply changing the stereo width of your sound can instantly make it (quite literally) more thicker. Look up M-ST stereo
plugin. Its free. If you don't know the difference between mono and stereo def need to research that.
~Exciters~ Exciters are used to boost (or rather excite) very high frequencies in a sound making them sound brighter. There is sort of a secret sauce a lot of welly developed
artist use. Use sparingly though. There are lots of free exciter plugins out there just google search
~white noise~ white noise is sorta that secret mold every major edm
artist uses to date. It's like a filler. And I myself don't like to use it too much, just because I like my sounds sounding more '
natural' idk hard to explain. But yea if you can add a little white nice to your lead either inside the synth itself, or using white noise generator and just layering a white noise over the notes of your lead, can work wonders. Make it subtle though.
~Distortion~ Distortion essentially amplify's your sound and then tone the color of the sound. Depending on which plugin you're using (there are soo many dist. plugins out there its unbelievable). Distortion is your best friend. Learn to use it wisely.
~unison~ Find this knob or parameter in your synthesizer and change how many voices there are. Common sense. Plain simple.
~Chorus/flanger~ essentially the same, learn to you chorus. Like the stefeh said.
~experimenting~ Not a vst. Just keep adjusting the sound and playing with it as much as possible and you'll get your desired effect.
Cheers mate. Happy music making