Changing rail fuses inside a B&K amp. Is it safe?

I need to change the rail fuses inside my B&K 200.5 amp. I have two channels which sound very fuzzy, almost no output, at any volume level. I changed the fuses in the back of the amp, for each channel, and it fixed a previous channel which was exhibiting the same behaviour. The two giving me grief now, were not fixed by changing the speaker output fuse, and I assume might be due to the internal rail fuses which are also a 6 amp slow blow.

The amp is probably nine years old.

My big concern is working around high voltage circuitry, and if it is safe to go in and change the fuses. Is this something I can and should do myself?