Processes and C/D box small nucleolar RNAs (snoRNAs) for altering telomerase activity and altering telomerase length are described. The processes of the invention involve the use of C/D box snoRNAs for targeted 2′-O-methylation modification of nucleotides in a pseudoknot region of the telomerase RNA. Depending on their position, the 2′-O-methylation modifications can cause an increase in telomerase activity and subsequent telomere lengthening or a decrease in telomerase activity and subsequent telomere shortening.