Depending on the operative system you are using you have to find "Language Options" and install Spanish (in Windows, I would recommend "Spanigh, Traditional Sort" or "Spanish, International Sort"). Once you have installed it, You have to change the settings to Spanish.
Here is a Spanish keyboard layout:
The diacritic you are looking for is next to "Ñ" which is next to "L". You have to press the accent key first and release it (nothing will happen), then you press any vowel key and the diacritic will show up on top of the vowel.
For the diaeresis (ü) you have to press Shift, without releasing it, press the acute accent key, then release both (nothing will happen), then press "u" and the two dots will appear on top of the "u". The letter "u" is the only vowel that would have diaeresis on it (pingüino, lingüística), if there are words that have vowels with this accent this they are foreign words.
I hope this helps.