I got mine off quite easily by using a hammer and drift, lay the crank spindle on some wood so you don’t damage the ‘teeth’ which join the two halves together and tap the bearing off the shaft, mine weren’t that tight, but had been fitted a lot less than 10 years!
For refitting the old ones, heat them up and just drop over the spindle and gently tap into place. To heat mine up I used a bearing heater (had one available at work) but I have used an oven in the past, you don’t want to take it much past about 110 degrees of heat though.
And make sure you remember to put all the seals on before fitting the bearings.
This may or may not sound possible depending upon your bike spannering skills?