A supplementing write-up to Akmal's post on Weight and Reaction
Generally, upgrading means buying lighter parts. In many cases, more efficient mechanism.
Those lighter one also has lower rolling resistance on bearing of the hub. Thus when we upgrade wheelset, we get lighter wheelset and also lower resistance hub than before. As a result, we pedaling up lighter bike and better power transfer right down to the tire.
Lighter & Better
Apart from wheelset, the following will also contributes to better you in cycling shall you unable to increase your power output (e.g by training more).
1. Change Crankset
2. Change Pedal
3. Change Tire
4. Change Chain
5. Adjust brake pad clearance to avoid rubbing.
6. Clean sludge on drivetrain (chain, cassette, and chainring) due to excessive lube.
I would suggest that you do 5 & 6 first since didn't cost money (maybe a little insignificant cost of brush & detergent). This maybe another good way to spend your non-riding weekend, after all.. it's Ramadhan.