FUSES VALUES: 250 volts VS 500 volts

I am planning to buy either ISOCLEAN fuses and the well regarded HIFI TUNING FUSES just to hear wich one react the best in my system.
I have a total of 9 fuses to replace some are the small(.79'') of 250 volts value but when it came with the larger HIFI TUNING fuses ( 1.26'')the voltage given is 500 volts...
My 9 stock fuses got a value of 250 volts the small one and the larger one.
I was told in the case of a stock 8 amp of 250 volt to choose a 4 amp with a value of 500 volt (Hifi Tuning fuse)?
So what should i do???
Your fuses need to match the current rating (amps) of the originals unless you are changing the circuit.

" VOLTAGE RATING: The voltage rating, as marked on a fuse indicates the fuse can be relied upon to safely interrupt its rated short circuit current. in a circuit where the voltage is equal to, or less than its rated voltage. This system of voltage rating is covered by N.E.C. regulations and is a requirement of Underwriters Laboratories as a protection against fire risk. The standard voltage ratings used by fuse manufacturers for most small dimension and midget fuses are 32, 125, 250 and 600. Short circuit interrupting capacities may vary with fuse design and range from 35 amperes AC for some 250V metric size (5 X 20mm) fuses up to 200,000 amperes AC for the 600V KLK-R series. information on other fuse series can be obtained from the factory. In electronic equipment with relatively low output power supplies and circuit impedance limiting short circuit currents to values of less than ten times the current rating of the fuse. It is common practice to specify fuses with 125 or 250 volt ratings for secondary circuit protection of 500 volts or higher.. As mentioned previously (See DERATING) fuses are sensitive to changes in current, not voltage maintaining their "states-quo" at any voltage from zero to maximum rating. It is not until the fuse wire reaches melting temperature and arcing occurs that the circuit volt age and available power influence the fuse performance and determine the safe interruption of the circuit. To summarize a fuse may be used at any voltage less than its voltage rating without detriment to its fusing characteristics, but may also be used at voltages higher than its certified voltage rating if the maximum power level available at the fuse under a "dead short" condition can only produce a low energy level non-destructive arc, fuses listed in accordance with UL Standard 198G are required to have an interrupting rating of 10,000 amperes with some exceptions (See STANDARDS SECTION) , which in many applications provides a safety factor far in excess of the short circuit currents available."
The amperage value is most important. Choose one that matches your stock fuse. As long as the voltage value is higher than recommended you are fine.
Use an 8 amp fuse, no more no less. If you were to use instead 4 amps you would be popping a 30 dollar fuse every time you try to power up.

Never ever listen to anyone contradicting the equipment manual or the manufacturer's tech support.
The voltage (as 4est wrote) is not important except the rating must be equal or higher. The AMP rating is all important. It should be EXACTLY the rating for the stock item.
The person who told you to halve the amp when doubling the voltage is wrong about FUSES!!
(That halving and doubling might apply to some other electical things, but NOT fuses)